The ruin is in fact the remains of the 21st century robotics and technology corporation Faro Automated Solutions, which was responsible for the creation of the Faro Plague, the army of combat automatons that overran the planet and exterminated all life. It was measures put in place before this happened, designed to restore life to the planet afterward and subsequent events thereafter which led to the world as it currently exists.
The ruin consists of the remains of several buildings, most notably a skyscraper that housed the corporation's main offices, including the office of the company's founder, owner, and chairman, Ted Faro, on the top floor. Presentation rooms for the the holographic presentation of FAS products are also present in the remains of the tower. Aloy saw presentations for the Machines known to the inhabitants of the new world as as Corruptors, Deathbringersand Metal Devils, learning of their origins as ancient war machines produced by FAS. There are also several Datapoints present, which Aloy found as she made her way up to Faro's office. These datapoints provide information as to FAS' lack of scruples, as well as hints of the Faro Plague. In Faro's office itself, she found datapoints which fully explained the origin of the Faro Plague and its eradication of all life on Earth.
A view of the FAS campus before the Faro Plague can be seen from a Vantage Point on the side of a mountain in the vicinity, left there by Bashar Mati.