Architect Phase Gate Facility

Alien Research Site Zero is an Alien Base near Research Base Zero. The top half of the base was a failed quarantine option for The Architects.

The exterior is built similarly to that of the Primary Containment Facility in the Crater, as seen in the concept art.

Story
During her search for Jo Jeffreys, Robin Goodall stops by Alien Research Site Zero, only to be denied access by an unknown voice, who threatens her. Taken aback by the facility knowing her name, Robin reports to her sister, Sam Goodall, who warns her that an electrical storm is coming, but lightning confirms that it's already arrived. On her way out of the cave, the electrical storm renders the cave unstable, and an avalanche blocks the cave entrance and destroys the Research Base Zero.

Lower Section - Alien Research Site Zero
The lower section of Alien Research Site Zero is accessed via an ice cave tunnel. At the beginning of the story, the interior is inaccessible as Al-An restricts access to the inside. At a later point in the story, presumably after Al-An has been given a physical form, the force field will be shut off, granting access. Not much is known about the contents of the base, except for a single elevator leading to the upper section of the base.

Upper Section - Shield Base
The upper section of Alien Research Site Zero is accessible only by the lower level's elevator. This section is known as the Shield Base, and is the endgame location of Subnautica: Below Zero. The Shield Base appears capable of generating a shield, but for what purpose is still unknown. It can be assumed that the shield will be activated in the later parts of the game. Al-An will be found here after the construction of his body.

In-development footage shows that a large amount of the base is jutting out of the mountain, forming what appears to be a balcony. The exterior of the upper section is far larger than that of the lower section, and it is possible that it may be visible from the surface. According to developer notes, the upper section features an Alien Arch leading to an unknown location, as well as a terminal that ends the game.

Trivia

 * The code to the first door is 4242, but inputting it does not open the door.