cave

n. natural underground tunnel, hollow opening in the ground

v. collapse, cease to resist, submit; cause to collapse; explore caves, spelunk

A cave is a natural underground void large enough for a human to enter. Some people suggest that the term 'cave' should only apply to cavities that have some part which does not receive daylight; however, in popular usage, the term includes smaller spaces like sea caves, rock shelters and grottos.
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A Cave Automatic Virtual Environment (better known by the recursive acronym CAVE) is an immersive virtual reality environment where projectors are directed to three, four, five or six of the walls of a room-sized cube. The name is also a reference to the allegory of the Cave in Plato’s Republic where a philosopher contemplates perception, reality and illusion.
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Noun
1. an underground enclosure with access from the surface of the ground or from the sea
(hypernym) enclosure, natural enclosure
(hyponym) cavern
(part-meronym) floor
(derivation) spelunk
Verb
1. hollow out as if making a cave or opening; "The river was caving the banks"
(synonym) undermine
(hypernym) hollow, hollow out, core out
(hyponym) sap
2. explore natural caves
(synonym) spelunk
(hypernym) explore

adj. hollow, sunken

n. cellar, cavern, vault

n. pit, quarry

adj. hollow, sunken