abandoned
adit
catacomb
cavern
channel
coal
collector
concept
concrete
corridor
danger
dark
decay
deep
derelict
digger
direction
dirt
dirty
drain
drainage
draining
environment
exploration
factory
flood
flooded
flow
flowing
industrial
inside
interior
leak
leakage
lost
mine
mineral
mining
mud
mystery
old mine
ore
outflow
passage
pipe
pipeline
pollution
reflection
resources
river
rock
round
sewage
sewer
sewerage
sludge
stink
stream
subterranean
toxic
tube
tunnel
underground
underpass
urban
vaulted
waste
wastewater
water