underground space; subterranean space
Refers to any space or cavity located below the ground surface, including natural caves, tunnels, basements, or underground facilities.
A vast underground space extends beneath this city.
Effective use of underground space is a challenge for urban planning.
地下室 specifically refers to a basement or cellar room, while 地下空間 is a broader term for any underground space.
地下街 is an underground shopping arcade, a specific type of developed underground space.
Compound of 地下 (underground) and 空間 (space). The kanji components are straightforward: 地 (earth), 下 (below), 空 (sky/empty), 間 (interval/space).