What your looking for is the secret chicken level, not the disco level, that's on the LOA map. The Utraean Penensula has this secret level. The link explains how to get there, and what you need to get inside.

no i'm really talking about disco level ------>
http://ds.heavengames.com/library/walkthrough/disco.html
i need 2 get in there !
Heeelp me please !

Yes, and as tieman said, the disco level is located on the new map that comes with the expansion pack, Isle of Utrae.

note the first thing it says

Note: The disco level exists on the new map that comes with the Legends of Aranna expansion, Isle of Utrae, and nowhere else.

wow look what we did when we read it all (lol)

Actually, I added that after quite a few people had misinterpreted it as if the level was on Utraean Peninsula. I think I addid it right after replying to this thread actually.