Secrets and mysteries in your game
One thing I have come to realize that I enjoy in games is the mystery of the game itself. I don't mean Mystery Dungeon style mystery where not figuring out something can make the game much harder on you, but stuff more just for fun (though the mystery of that game IS very appealing, same as with games like NetHack). For a multiplayer game, people will probably be more irritated than anything if they realize that there is something they could have been doing that would make them progress much faster. As a result, a lot of people do just read up on the best places to level for level X, best attacks for certain monsters, different combinations to use for crafting items, etc.
Creating the mystery
First, how do you present these mysteries to your game? For me, if I feel like I know all there is about a game, there is a good chance I'd grow bored of it very fast. Super Metroid was fun because there was hidden crap everywhere, most of which was just a tiny benefit. The designers did a good job keeping it more than just finding out what blocks to hit with what weapon, or what wall to jump through. But a lot of that was "twitch"-based, which is no surprise since it is a twitch-based game. And requiring precise timing for an internet game, especially one not designed to be twitch-based, can lead to annoyance more than anything.
Top-down RPGs seem to have it "easier". It could be because they are far more common for online RPGs so we just have more exposure to the ideas, along with that side-scrollers are usually action-oriented and utilize the twitch-based aspect to reach secrets. Walls you can walk through are much easier to achieve in top-down and usually fit in quite well, as shown numerous times in Final Fantasy back when it was worth playing, along with many others. There are also the walls or hidden switches you can "use" to open a passage. This works especially well in a game that utilizes the ability to only show rooms or areas that you are currently in instead of the whole map at once. This all applies to side-scrollers, too, but unless you want people trying to perform difficult jumps, it can be a bit tougher to work with.
You also have to keep in mind what the client knows. Multiplayer games give you the unique ability to hide information from the clients, but if you have walls that are not blocked (information that has to reside on the client), people can use third-party tools to view this. However, most everything else is good to go. It could be a simple invisible teleport, triggers, or just idling in the right place for long enough.
There are countless ways to put secrets into your game other than the overly-used non-blocked walls or invisible walls. But it needs a good combination of originality, creativity, and difficulty. Its also nice if it makes sense, either as part of the story or something plausible, not just a random teleporter in the sky for no apparent reason.
What is the point?
Just as important is the point of the mystery. Being absolutely pointless is fine in some cases. Many games do this as easter eggs. It can also be an inside joke ("Its Bill's Fault"). But those usually just short-lived entertainment. As I mentioned before, if it gives much of an advantage, everyone is going to want to know about it, and not knowing about it will probably lead people to being annoyed. It sucks to be sitting there desperately trying to kill a monster while someone else the same level as you runs by slaughtering them all just since they knew about a secret passage leading to a better item or some perk. But not giving them anything will just result in most not really caring since multiplayer RPG players are notoriously bad at taking time to actually enjoy the game at any pace and would instead prefer to grind non-stop and try to be the best.
Stuff that you can show off is usually a good reward, like items that are equal to or only slightly better than what they would normally have. You can also have items that are just flashy such as fireworks, or spawn a guy with a camera that falls down from the sky and makes everyone say "Fuzzy pickles!" I have seen achievements being used for stuff like this quite a lot recently, though I don't think I'm really a fan of that approach. It makes it well-known by everyone who is trying to get all the achievements, which brings up the next point:
Keeping the secret
Probably the most heavily utilized form of mystery in games are either recipes for any form of crafting (alchemy, smithing, etc) and secret areas. Both of these also remain static in every game I have seen (the recipe to create a health potion is always the same). Once someone publishes it, the secret is gone. Since plenty of people love to publish everything about games they enjoy, fan-sites pop up all over containing just about everything about the game. All of the sudden, your game full of mystery just looks like some game with a bunch of holes in the map. There may be some other stuff out there that nobody has published, but who cares?
As mentioned earlier, keeping things server-side is a good start. Anything the client knows, the player can extract. Games that keep a database of item and NPC stats on the client usually end up with a published list of all that information for everyone to see. But where do you go from there?
This one I am not too sure about. Dynamically generating secret areas could work, and would be very easy to implement into a top-down game by utilizing non-blocked walls. But then you don't really have more secrets, just a secret that moves around. It could work for a few specific things, but definitely not a panacea. This would place it more in the category of a different type of secret, not keeping something a secret (other than the location, which then is a secret, but not really mysterious). The first person to discover an area can also be rewarded in some way, such as putting a sign or flag up with their name on it, but then you are running into the problem of either having to design tons of secret areas, or only letting a few people ever be a discoverer (which isn't exactly a bad thing). Making it so the area closes off or the reward is taken from the last person to discover the area and given to the new discoverer just leads to annoying little competitions and/or people just telling their friends.
Something I don't see very often is complexity with the secrets. This falls a bit into the first issue (creating the mystery), but also fits in here. You can find a secret area, acquire the reward(s), but still not know how it works. As a simple example, imagine a top-down game where you have 4 vertical rows that are aligned, equal size, parallel, and blocked off from one another. In the right-most row, at the top, there is a crystal (or whatever "magical" object you want). In the left-most row, at the bottom, a button on the floor. Every hour, the crystal starts to turn red for a few seconds the spews out a monster into the right-most row. The monsters run away from one another, so the spawned monster runs to the top while the monster that was there before (if any) runs to the bottom. If there was no monster there already, it just hangs out near the top. At the bottom, you have a teleport leading to the top of the next row (one to the left). When a monster touches the button, they all die and the treasure for the room respawns. Congratulations, you just made an in-game binary adding machine attached to a timer.
While that isn't hard to figure out, I hope it gives the idea of what I am talking about.
Well, my long rant is over. If anyone manages to make it through that, I'm interested to hear what others come up with.
I think achievements are a good idea. I still feel like secrets are good too, but they get spoiled so often. (actually, they get spoiled every time pretty much... or at least the ones that matter)
This reminds me of the "How to catch mew" "glitch" (apparently it was put in by the developer Tajiri 
) http://www.ocf.berkeley.edu/~jdonald/pokemon/mewglitch.html if you scroll down it shows you how the glitch is working in the memory.
There are 10 types of people in this world - Those who understand Binary and those who don't.
Sorry to say but mystery in online games is impossible for one reason: The internet.
Same reason I could never win the tournies of magic the gathering as a kid: The internet.
Lets face it. People don't just go through an online game like they do a single player game. They have to know the fastest way to the top and they have to know where every single secret whatever and the best items are. To do this people post guides on the internet and very soon any secrets your game had are now common knowledge to everyone.
As for Magic. Well it always suprised me as a kid to see people with such simular decks while I created my own unique decks. I never suspected as a kid though that everyone was simply going on the internet and copying what the pro's were using at the time.
So much for originally.
Sure, the secret does get ruined, but like I said there must be some ways to motivate people to keep it to their self. Mercenaries of Astonia was a good example of such a game. It was a relatively small game, but there were plenty of hidden chests and such. Over time, yeah, everyone did start to learn about them. But for a good part, people just didn't really "advertise" it since they wanted the items for their self. Each chest respawned about once an hour, and once someone grabbed it, the item was gone. Not like games today where the chest lets everyone loot it once.
Also, it takes time for word to spread. For a MMO, its a different story. But for an indy game, you have to take advantage of your lack of a population if you want to compete. Its not like someone finds something, instantly opens up their browser and posts it for everyone to see, especially when you have some way to help discourage that. Its just a matter of coming up with a way to discourage it while still keeping things fun and fair.
Just wanna point out that this might be something that should not even be thought about until your game is mostly complete. 
On the other hand RPGs "secrets" have always been what's made or broken a game in many cases. The secret cow level in Diablo 2, party quests in Maplestory, missingno for Pokemon. Although the other thing these had in common was not just the secret-ness of them, but also that they had huge benefits and replay value.
The secret cow level allowed you to get SOJs which was the economy of D2 on B.NET and also set-items, however killing the cow king meant you could never go back so you couldn't just AoE the entire cow army in 5 seconds. And killing masses of axe wielding cows is just fun.
Party Quests in Maplestory gave you tonnes of experience points while giving you a break from the daily grind, you could earn points from solving puzzles with your party, and eventually it would unlock a huge boss which you had to team up to kill.
Missingno was probably the worst one, but this was at a time before most people had decent internet and it was mostly that eureka moment from being told by your friends. The value of it was that even if you mass rare-candied your pokemon, it didn't mean that it was the strongest it could ever be, so you could restart the game and roll the dice to see how strong you could get your mew two for instance.
It doesn't matter if people find out on the internet, honestly its better if everyone knows about it and can use it to their advantage thus leveling the playing field, than having some guy roll you just for knowing all the secrets. As long as you have enough of them, people will still find secrets on their own. At the same time, the best secrets should be known to everyone, because they add replay value to the game. What use is a secret that makes the game more fun to play if people will never find out about them.
Not sure I'd agree with that, since it can be a major part of your gameplay or game appeal.
But then you are going under the assumption that knowing the secret serves as an advantage, or at least a notable advantage.
There is a big difference between finding out about something for yourself and just being told about it.
I think the majority of secrets should really only be made in the intention of not being kept secret. (if that makes much sense) Like a portal to another map that makes it faster to get to. Little stuff like that rewards people for exploring the map instead of following the paved roads all the time. So what if someone goes and posts it on the internet. The players who go and read it will start using that passage way and they will see the scenery.
That doesn't really work for everything. I just thought of it for that sole reason.
Using personal greed/interest for keeping secrets um... secret might work. (it'll spread over time, to the point that it'll be common knowledge; but it'll take time which is Spodi's point)
Really, I think anything rewarding should take an effort that is worth rewarding. Why in the world should my character walk past a cave and think, "Hey a cave! Maybe there will be a giant sword of awesome power!"... (unless that's part of the storyline, but you get what I mean) This just applies to items with serious advantages though... nothing like a treasure chest.
All in all, I think every secret should be implemented differently. A little of everything doesn't hurt. Innovation breeds fun.
If you want to just have flat secrets, then just have flat secrets. If you want innovative, fun, secretive secrets, use your noggin.
Not sure I'd agree with that, since it can be a major part of your gameplay or game appeal.
Your first point relates to the last thing you quoted from my post. If you keep the best parts of your game so secret that only a few people can find out about them, then how can it be a "major part of your gameplay or game appeal"?
In other words, it doesn't make sense to have a game based on secrets, Saying that the secrets will be a "major part of gameplay or game appeal" to me sounds like all the effort will be put into stuff that never gets found, and therefore people will just think the game is crap.
The major part of your gameplay or game appeal should come from content (that can be found easily) and game mechanics, yes? Otherwise people would just think the game has nothing. Unless they find out on the internet, but then they found out the secrets on the internet, which is also what you don't want.
EDIT: Maybe I should just point out that with almost all successful games, secrets and easter eggs (the sort that you mentioned) are most often thought of and implemented nearing the end of the development rather than being theory-crafted in the beginning. Often because inside jokes will develop during the beta and then they will materialise these jokes, or just because its not a high priority for games in early-mid development.
But then you are going under the assumption that knowing the secret serves as an advantage, or at least a notable advantage.
Well, because they usually do, otherwise people wouldn't bother or maybe just do it once for the lulz.
This was actually for Ellimist who was implying that the internet ends up turning secrets into necessities thus making secrets bad. That said, do you plan on making a game with secrets that form "a major part of your gameplay or game appeal" but don't give any advantages at all? There will always be some and they can easily be found on the internet.
There is a big difference between finding out about something for yourself and just being told about it.
There is, but that doesn't mean that people won't get told about it, your eyes and ears don't have in-built spoiler blockers.
Like I said, as long as you have enough of them, people will still find secrets on their own. The best secrets will always be found on the internet, and if it forms a "major part of your gameplay or game appeal", then its probably a good thing. Also, this is something that can't be helped, and I think people should look from that perspective, rather than assuming that not a single soul in the world would dare to look on the internet in fear of having the game become less fun.
I think you kinda missed the whole gist of my argument though. I'm not saying secrets are bad, secrets are fine, but don't expect people not to look on the internet, so they should be fun even if they are spoiled (and often the best ones are)
Again, just because it is a secret, that does not mean people won't find it. Roguelikes, like NetHack, do a good job at making the secrets of the game a major aspect of it. Many fans of those kinds of games consider looking up information about the game (other than your general help) synonymous with cheating. Not saying it'd be a good idea for a multiplayer game, but just saying that its perfectly reasonable.
And wouldn't this fall into "content", and depending on how its done, even "game mechanics"? I left things quite general intentionally in my initial post since there is a huge variety of ways you can do this, some of which have almost no impact on the game while others define a major part of it.
Not really. Even as just an incredibly unoriginal example, if you had a little side-quest that took about 20 minutes to complete, and gave about the equivalent of if they were to be grinding for 40 minutes, that is about a 20 minute gain. Does that give a notable advantage? Definitely not. Unless you were in some kind of "race" with leveling, in which case knowing the secrets of the game is clearly a vital aspect to "win".
Who said you'd do both of those at the same time? Clearly, that'd be a horrible idea.
And that was one of the major points of my original post - how to keep things mysterious even when its not a secret. Instead of straight-forward, unoriginal crap that you see everywhere like "room with treasure chest; loot chest; profit", do something that no one person could easily figure out on their own. Let discussion spark on the meaning behind it, how it works, etc. It may not be very secret, but it still retains the mystery.
Though it probably doesn't help that I used "secret" and "mystery" interchangeably at times. What can I say - it was early.
Definitely true, and that was the primary reason I started this thread - to see if we could get some original ideas flowing, not so much debating about the importance of mystery in your game like this thread has turned into.
Tibia has these, they have a powerful sword in full view on the noob island, but it's surrounded by water and no one knows why it's there alot of people think there's a secret way to get it, and people are always trying
Who knows
That kind of stuff I have always thought of as being a good way to entice new players. Not a sword exactly (unless its one badass looking sword surrounded in badassery), but teasers of high-level stuff early on. This is probably a really bad example that hardly anyone will get, but the boat in Final Fantasy Mystic Quest was an example of this for me. Its just a stupid boat, but its sitting on the side of the cliff, and for some reason, I wanted to know what the purpose of that stupid thing was for. Then again, its been so long that I could be completely mistaken. Meh, you get the idea.
This is probably the only reason I stuck through playing Risen. Early on, you can run into an Orc (or some similar creature, forget what it is exactly) that just completely destroys you. Clearly, you're not supposed to take that path. But you can run by him easily enough and see this giant, "magic"-like cave. You can't anything in it really, but there was clearly stuff to be done. If I remember correctly (which I probably don't), there was some giant gap with a chest or something on the other side. Throughout the game, I kept thinking back to that cave, wondering what the hell it was for. I completely fail to describe how enticing it was, but that is because I hardly remember. Finally found out pretty much at the very end of the game that it is for the final armor/weapon set. That was pretty much the last mysterious thing about the game, so once I found that out, I hardly cared to finish.
Who knows
How do you know its powerful? It could be like the masses of gold and items in the underground vault in Runescape. Its always there taunting you, and you never know how to get it. Then you decide to go a mage and realise theres a spell which can teleport items back to you, you decide to give it a shot and see if you can steal some awesome loot from the bank, only to realise the items were in fact... shit.
I prefer storyling secrets because when you find them it gives you no real benefit but perhaps some insight into something you didn't know.
Like ive been playing Aion and players farm this flaming demon boss called kromede. Well they added a solo instance where you play as kromede and find out that she is infact a good guy who was setup and basically is just really pissed by the end of it.
Or like finding out that nemesis in resident evil 3 is actually the mutated corpse of the main character from one of the earlier games.
Actually im really surprised that mmorpg's in this day and age still fail to provide decent storytelling considering that for the most part they are still RPG's with little actual action game-play. I can't personally think of a way to add good storyline in netgore (sorry but almost noone reads the npc text. Voice overs and cutscenes are a must.) But I like to think of my netgore project as something easily done by an indie group so that in the future we may create a higher budget title.
Anyways I think that "secrets" as you guys talk about are more like what I call "tricks". I think of "secrets" in my games more like "mystery" or hidden elements that even if found aren't easily repeatable or don't have significant enough value for people to actively share or seek out on the internet.
You could always code or design a nice little secret that has limited uses or is active for a limited time only.
I should have specified, it's easy to get in the mainland, and it's not too valuable there and rather common, but in the noob island (which you can't go back to ever again) it would be extremely valuable because obviously there are only a few weapons available.
There are people who stay on the noob island and just live there, getting to levels like 70+.
http://tibia.wikia.com/wiki/Sword_of_Fury
Read about it there, it's an excellent way to get all the noobs interested. There are loads of things like that on Tibia.
Actually, reminding me, you could keep a mystery secret by giving players an incentive to make their own (like bury their own treasures and leave clues) In Tibia you can get a blank book and write on it, I used to drop them like diary's and leave cryptic messages to where I left some loot.
As to how to convince someone to do this.. No idea, but it was fun for me.
Hehe. Tanar uses an invisible drop that only one or two people have figured out. It was quite fun. The item starts a quest at one of our normal npcs that's pretty fun. So unless you for some reason decided to try and pick up the nothing that dropped you would never know.
I played FF7 about a year ago just for that reason... well that, and the little mini-arcade.
Secrets should just be fun/insightful. Not really advantageous. That's just my opinion.
I feel like letting players leave treasures and stuff like that behind would be cool. I'm not sure why I would do it in the first place though...
OMG Earthbound reference spotted!
As for secrets, I really haven't thought of them, you can't really keep any secrets in MMORPGs or any games for that matter for the reasons you explained. Hence why we're going with achievements in SVO.
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