History: EVOLV's agricultural initiatives lead to the development of plant fertilizer out of sulfur from the island's volcano. In order to create more plant fertilizer, the volcano is actively mined.
Rachel's detour back to the front of EVOLV leads to a dead end. There is a cave, and no other way forward except through it. She must use the cave tunnels to reach the other side of the island.
Deep in the cave, things get spooky. The cave is pitch black, but some of it is navigable due to the frequency and positions of torches. Dark parts can also be traversed, but it's nearly impossible without sight. Following the torches eventually leads to the discovery of an item. This item can be used to overcome the darkness and explore new areas.
Once Rachel can see everything, it becomes apparent she's surrounded by horror. The walls are stacked with bones in all sorts of configurations. There are some artifacts and statues with inscriptions. Rachel's ability to shed light opened up a whole new set of puzzles involving bones.
Once the mysteries of the catacombs are overcome, Rachel is able to unlock the path to the exit. She steps into the swamp.