Here's a little YouTube clip from the Mickey Mouse animation titled 'The Mad Doctor'.  The section in particular that I like is when he's walking down the narrow tunnel.

Created in 1933 it shows a brilliant understanding of depth by the animator.  It's been done so well that you really get the feeling of a moving, flowing camera.  It's similar to a manoeuvre you'd see from a live action film.

Thoughts by,
Sian