The Halocryst Chasm Sector

The Halocryst Chasm Sector is an underground region of tunnels and caverns not far from the colony city of Indinapolis, on the edge of that settlement's control. There is one particular bastion of human civilization, Outpost Theta. Beyond this to the south and east is effectively subterranean wilderness. 

The Halocryst Chasm, after which the sector is named, is a massive rift, about 200m wide and running for about 7km from northeast to southwest. Nobody is sure how deep it is, but it is believed to be at least a kilometre straight down. The humans from Outpost Theta have not yet bridged this, even though there is a matching tunnel on the other side, suggesting that the tunnel formed first then the chasm was created, making a break in the tunnel. They probably could but there is great caution about what is on the other side and whether unknown enemies could use a new bridge across the chasm to threaten Outpost Theta. 

The Atlas Mines are owned and run by the Atlas corporation. Although the main tunnels are shown on the map there are many unmarked smaller mineshafts and tunnels, turning the Atlas Mines into quite a maze. The mines produce metal ores for Indinapolis and the Atlas corporation is keen to keep them functioning and profitable. Security guards are sometimes deployed because of wildlife infestations (including spined rats) in the darker recesses of the mines that sometimes attack the miners. 

Jawbreaker's Camp is outside the jursidiction of any colonial city and is a refuge for those who have left Indinapolis for one reason or another - usually fugitives avoiding the law. Jawbreaker was the bandit chief who established the camp and turned it from a squalid hideout into a town with its own rules and trade and a population of 600 humans. 

The Living Caves are a series of natural caves that contain an ecosystem of Xenophytes with accompanying fauna, mostly native rather than colonial. Academics are interested in studying this environment but others reckon there are mineral resources here to be exploited, regardless of the effect this might have on the wildlife. 

The Verminous Tunnels are similar to the Living Caves but while several expeditions from Indinapolis have visited the Living Caves, only one has traversed the Halocryst Chasm to reach the Verminous Tunnels. And then they wished they hadn't. Less than half the personnel made it back across the Halocryst Chasm alive. They had encountered a native ecosystem but the creatures there were hyper-aggressive and very predatory.