covert
subsurface
underground railway
Amtrak
Charley
L
Paris
Trojan horse
Tube
VC
Vietcong
abstruse
agreement to disagree
alienated
alienation
alternative
antiestablishment
apostasy
at odds with
at rest
at variance with
avant-garde
back door
back stairs
back way
back-door
backstairs
baggage train
beclouded
behind the curtain
behind the scenes
behind the veil
below
blind
bolt-hole
branch
breakaway
buried
bushfighter
bushwhacker
cable railroad
cable railway
casual
catachthonian
choo-choo
clandestine
clandestinely
close
clouded
cog railroad
cog railway
railroad
railroad line
railway
railway line
railway system
central
extensive
industrial
inner
nearby
subterranean
vast
western