Snails have eyes on the tips of their tentacles. In the case of the Pulmonates [lung breathers] who have two pairs of tentacles, the eyes sit at the tip of the top pair.

Capertee Valley Corrugated Snail Sauroconcha caperteeana

Snails have very poor vision. Even though they have a lens on their eye, they have no muscles to focus the images. They can sense light and dark and work out where the light source is. They cannot see colour. 

For more information about snail eye anatomy, go to this website: