It's probably found by Rhombus during seeking a main base of operation for the crusade against Attis Super mutants. The place appears to be a Vault-Tec property, probably a facility dedicated to the Secret Vault project, a vault prototype. Some valuable technology and inventory, like working computers, laser grids, functional steam pipes, radioactive drums, Gun Bots and holographic devices were found there and used for training new initiates.
In the game, Nadia completes this course, guided by a Paladin hologram, while various people in Vault uniform watches on her progress. These people are probably the Texas Brotherhood of Steel members who simply uses the uniform found in this location.