That, my friends, is an arboreal snail_ Megastaunia imperator
I mean, why have a shell to protect yourself, and then put your body on top? hmmmm, I could not find any good answers to this, but most seem to revolve around a)humidity makes this possible, and b)it is halfway evolved from a slug. A snug?
Mostly found climbing on walls and trees, (hence the name) these are nonetheless land snails, and are part of a group of land-dwelling gastropods that have the ability to breathe air. Terrestrial snails include more than just snails, they also include slugs (which are very similar to snails except they lack a shell).
Terrestrial snails are one of the most diverse groups of animals alive today, both in terms of their variety of form and the sheer number of species that exist. Today, there are more than 40,000 living species of terrestrial snails.