I wouldn't sail this ship if I were you
7099 Things beneath the surface of the Earth
-7099.1 Caves and their inhabitants
–7099.11 The sandy-bottomed caves of containable peril and their gentle, bucolic tour guides
–7099.12 Sea caves that are full of old stories washed smooth and round
–7099.13 Those caves that have hidden depths
–7099.14 Caves that draw you in with the siren song of one more crystalline chamber or cathedral arch or echoing shaft or treasure chest or sheaf of crumbling paper, the call of the ancient and unseen, and they never quite deliver but just enough to keep you going back and back and back and back again, and the cave sits at the back of your dreams, working your subconscious like a machine to find new ways to corkscrew round that final obstruction, and it whispers that you will die there and somehow this does not seem so bad
–7099.15 Pale beings with wormlike fingers, counting up time with their heartbeats until they can come up
–7099.16 It’s just a cave you guys of course we can sleep here tonight what’s the worst that could happen?
-7099.2 Basements, cellars and holes and their inhabitants.
–7099.21 Dingy and depressing flats
–7099.22 The secret basements of billionaires
–7099.23 Nuclear bunkers
-7099.3 Tunnels for human use
–7099.31 Subway systems
-7099.3 Tunnels for animal use
–7099.31 Lairs, dens and suchlike
–7099.32 Things that look like caves but are actually unusually large gullets
–7099.33 Things that look like caves but are actually unusually large orifices (non-gullet)
-7099.4 Tunnels for the use of eldritch beasts
–7099.41 Those that run beneath Washington D.C.
-7099.5 Underground lakes
–7099.51 Those that glow with a sinister light
–7099.52 Those into which you have just dropped your camera
-7099.6 Buried items
–7099.61 Alive
–7099.62 Dead
–7099.63 Schrodinger’s zombie and its fascinating friends
–7099.64 Treasure
–7099.65 Cheese and butter
-7099.7 Magma and suchlike
–7099.71 The stuff at the very centre of the Earth