The above described techniques of keeping secrets won''t work. Relying on a special key to get access to the secret, what would stop the one that finds the key from telling others where it is?

If the way of finding the key was different for every player, the secret would be kept for ever, mostly. Some people would of course search the world for it, because someone else told them that it exists, and maybe some others confirmed that they found it in different places... This is not a very fun way of keeping secrets though, as you can only place the key at a random(maybe a little intelligent) location. Not at some predefined, really hard to find location, that made someone chuckle while setting it up.

Secrets is not really something you can have in massive multiplayer games.

Oh, and by the way, how many here knows of the secret in Half-Life on the map crossfire ? I can only get there by noclipping, there''s a button that supposedly opens it inside, but outside... I''ll have to decompile/dump ents,

Well, if you make the key in limited number than it gets interesting When people are done with the quest they can hide the key somewhere for the next player to find and make their own quest for the player where to find it. If they want to of course.

Like your guild could have a storeroom with a password and the best equipment in there. The password, instead of being an actual password, can be a piece of knowledge that you pass around like an item. But if you give someone else the password you still have it. Could lead to intrigue.

If you have to tell players the secrets by actually finding their characters and giving them the secrets, that helps limit secret spread. And for the most difficult places to find, you can use the key system where there may only be one key in existance.