What are some optical illusions that you know of?

Question: What are some optical illusions that you know of!?
Best Answer - Chosen by Asker:

The most famous one I can remember was in the movie Labyrinth!. Where a certain creature says to go forward in the maze where its a wall to the main character, Sara!. Sara tries to go forward and is surprised that there is an opening in the wall revealing another layer of a wall (around the back) thats makes the front wall as if there was no opening!.Www@QuestionHome@Com