Alien Bases

Precursor Bases are in-development stuctures. They were built by the Precursor race, and are to be located within the Mountain Island, Inactive Lava Zone, Active Lava Zone, and the Lost River.

Locations
By the Mountain Island a huge tower built by the Precursors will be present, atop this tower is a large "gun"

Trivia

 * On a Trello card the Precursor "Gun" was referred to as the Precursor G.U.N, or "Precursor Global Defense System". This is a developer joke as "guns are not allowed in Subnautica" yet the model's name is Precursor G.U.N.
 * Models for the Precursor Bases were indirectly revealed during an experimental patch. After users on Discord revealed screenshots of the bases, the developers quickly removed them, and said it was "a huge screw up".