You're on the last treasure. Go back to the snake room and head SW. Yeah, I know, you'd have to guess every direction in every room to find this one. Head east to the dragon. The inanity gets even better. Say KILL DRAGON. It'll ask you if you just want to use your bare hands. Say YES. You kill him! Take the rug.

You can head north to realize that that window you've been madly trying to "solve" west of Y2 is just a mirror. You'll see a pretty reservoir. Nothing else up here though. Bring the rug back to the room, and you now have all the treasures.

Adventure - Colossal Caves Walkthrough
Master Walkthrough Index