Inactive Lava Zone

The Inactive Lava Zone (ILZ) is a cavernous biome located 900 meters below the surface. It is the third deepest biome in Subnautica.

Description
The Inactive Lava Zone is characterized by large, arching structures and walls of hardened lava with occasional steaming lava streams. It is composed of two distinct areas and can be found at 900 to 1300 meters down, well below the limit of a Seamoth (even when equipped with a Seamoth Depth Module MK3) - making an upgraded Cyclops and Prawn Suit the only vehicles to be able to navigate through it. The Player must be extremely careful when navigating this biome, as touching the lava on the floor of the Inactive Lava Zone will result in immediate death and the temperature applies constant damage. It also contains the rare resource Kyanite, which is used in crafting some Prawn Suit and Cyclops modules, which can only be found as a Large Resource Deposit here, meaning the player needs the Prawn Suit Drill Arm in order to get this item.

At the center of the Inactive Lava Zone is a large chamber, with occasional veins of lava and spires of hardened rock. Lava rivers can be found in narrow corridors around the area. A large structure called the Lava Castle can be found in the middle of the Chamber, with small, partially-collapsed volcanic domes scattered all over the floor of the Chamber itself. Many skeletal remains of Reaper Leviathans can be found here due to the Sea Dragon Leviathans infrequently coming to the surface to hunt them and bring them to the central chamber to feast.

Near the Lava Castle, There are multiple lava falls, leading directly into the Lava Lakes. They can be found easily by following the streams of molten lava on the floor of the Chamber.

The Lava Pit is a large pit found on the outskirts of the main chamber. The walls of the pit are covered in large grooves, one of which acts as an entrance to the Lava Lakes. The lighting in this area is much brighter than the surrounding areas of the Inactive Lava Zone. It resembles a volcanic dome.

Trivia

 * There was once a corridor leading to the Inactive Lava Zone that was found in the Crash Zone.