Subterranean

Subterranean is the final region in the game, and consists mostly of long tram tunnels filled with dilapidated trains. The dark pipes of the Filtration System connect these tunnels to the caves of the Depths. If the player reaches this region before upgrading their max Karma to the highest level (10), their progression will be stopped by the Guardians in the Depths.

Creatures
The following creatures may be found in Subterranean on easy and medium difficulties:
 * Big Spiders
 * Centipedes
 * Dropwigs
 * Guardians (only in Depths)
 * Jetfish
 * Leviathan (only one, found near Shoreline gate)
 * Lizards
 * Black
 * Blue
 * Green
 * Magenta
 * Salamanders
 * Miros Birds
 * Monster Kelp
 * Scavengers
 * Worm Grass

Additionally, the following creatures can be found in this region on hard difficulty:
 * Cyan Lizards
 * Red Centipedes
 * Spitter Spiders

Echoes

 * Two Sprouts, Twelve Brackets (Located near the Farm Arrays gate.)

List of Karma Gates to other regions

 * Gate to Shoreline - Requires 2 Karma.Located at the rightmost point of Subterranean.
 * Gate to Drainage System - Requires 1 Karma. Located at the uppermost point of Filtration System.
 * Gate to Farm Arrays - Requires 5 Karma. Located at the leftmost upper point of Subterranean. This gate is intended to be one-way, but clever use of spears or bringing a squidcada or grappling worm may allow the player to travel through from Subterranean.

Subregions

 * Filtration System
 * Depths

Trivia

 * When entering this region from Farm Arrays, you have to jump off a cliff. This is a one-way trip, but there are several easily missable items of interest on the way down. Down the right side is an echo which will increase your max karma. A crimson colored pearl can be found half-way down the left side off the cliff, that is difficult to reach. You may make a long jump from the top of the cliff or throw explosives to blast the pearl off.
 * Filtration System can only be traversed safely with a light, which can be obtained either through consuming a Neuron Fly or by trading a Scavenger Merchant for a lantern.

Map in Game

 * Download all .png in-game maps here.