It was a large indoor environment with different close-quarters environments, including small buildings and tight corridors, that was used by "veteran instructors" to train UNSC forces.
On the top floors of two three storey buildings were mock-ups of Jackal Snipers. Devices were also built into some of the walls that when triggered by nearby movement, display silhouettes of armed Brutes, supposedly to simulate a combat environment. It is used by instructors who favored hands on combat training, as opposed to a simple rifle/firing range, or illusory simulators.
It had several labeled training sections, including M1, K1, and K2.