cave
/kāv/
noun
a large underground chamber, typically of natural origin, in a hillside or cliff.
"the narrow gorge contains a series of prehistoric caves"
synonyms: cavern, grotto, hollow, cavity, pothole, underground chamber, gallery, tunnel, dugout
verb
- explore caves as a sport."they say they cave for the adventure, challenge, and physical exercise"
- capitulate or submit under pressure; cave in."he caved because his position had become untenable"synonyms: collapse, fall in, give, give way, crumble, crumple, disintegrate, subside, fall down, sag, slump
A cave or cavern is a natural void under the Earth's surface. Caves often form by the weathering of rock and often extend deep underground. Exogene caves are smaller openings that extend a relatively short distance underground. Caves which extend... Wikipedia
Most common type: karst caves