地下洞穴
underground cavern
underground cave
underground cavity
Subterranean
洞穴
Habitual den
cave
burrow
vault
Den
grot
Grotto
Microorganism
lacuna
cavern
Grott
elastic wave reflection
Cavity
UNDERMINE
Caves
burrowing
Burrrow
Dens
caustic wash treating
Hole
洞穴沉积
cave sediments
spelean deposit
cave deposits
洞穴沉积物
cave sediment
cave deposits
Speleothem
Speleothems
洞穴充填
cavity filling
cavern filling