In nature, what is an eyestalk?

I would like two eyestalks on the top of my head. Good for extra vision, but hard to buy a hat.

Pulmonate land snails usually have two sets of tentacles on their head: the upper pair have an eye at the end; the lower pair are for olfaction. Lobsters and some flies also have visual eyestalks as opposed to olfactory ones.

TRUE CANADIAN Laurel, If the stalks were prehensile they would be like varifocals