ive recentle downloaded the fly patch. when you first see the keep fly directly up. you should find the locked myst book that you can only see the front but when you look from the back you can only see the edges. I know that its not exactlyan easter egg but its interesting.

Throughout the game, you can use fly mode to find objects that play a role in the game (books, pages, some cubes, and also Esher, Yeesha and the Bahro).