The subterranean ecology of Gaeleth exists almost entirely free of the surface world, with only some of its energy flow deriving from the surface world. Most of the energy is derived from chemosynthetic bacteria that decompose the rock, some amalgams of which are considered quite dangerous, such as the highly acidic 'black puddings'.

Example encounters in subterranean environments includes (but is not limited to):

Black Puddings (4E Dungeons and Dragons Monster Manual II)
Carrion Crawlers (4E Dungeons and Dragons Monster Manual)
Cave Fishers
Tunnel Worms
Albino Lizards
Trappers
Omsomivae
Myconids (4E Dungeons and Dragons Monster Manual II)
Jermlains
Piercers
Smithbanes (aka Rust Monsters) (4E Dungeons and Dragons Monster Manual II)