covert
subsurface
underground
basaltic
dank
dead-end
dimly-lighted
disused
dome-shaped
filled-up
funnel-shaped
high-ceilinged
high-vaulted
innermost
labyrinthine
low-roofed
man-made
night-dark
roofless
stalactite
subterranean
sunless
tortuous
twilit
two-roomed
windowless