The Mountains is a vast biome known for huge deep underwater mountains ranges, hydrothermal vents, rocky structures and an abundance of brown algae. It is located northeast of Lifepod 5, bordering the Koosh Zone, one of the Mushroom Forests, the Underwater Islands, one of the Kelp Forests, and the void.
The Mountain Island, located in the southwest corner of the biome, extends 110 meters into the air above the sea level, featuring many underwater Mountain Range Caves that can be both entered from the underwater entrance or directly on the island's shore. The foundation and underwater entrance of the Quarantine Enforcement Platform can be found on the northern side of the Mountain Island.
Players must take extreme precautions while exploring the Mountains, as it is also home to location of six Reaper Leviathans. At least one can be found near the island bordering the Mushroom Forest. Wreck 5 can be found here.
- In early development, the Mountains was planned to be an entrance to the Lost River.