Subterranea
underground space, natural and man-made underground structures
underground lake
salt cavern
subterranean river
rock-cut architecture
subway
underground structure
deep geological repository
underground city
burial vault
storm cellar
Svalbard Global Seed Vault
cavern
volcanic pipe
basement
underground parking space
underground storage
lunar lava tube
lava tube
sump
London deep-level shelters
cave
crawl space
Stepney Green cavern
Almería air raid shelters
Camden Catacombs
Cueva de Conan
Kingsway telephone exchange
cave system
hypogeum
wine cave
missile launch facility
casemate
dungeon
dugout
Los Angeles Mall