Since the main entrance is collapsed, the tunnel is entered through a door built into a wall on the side. There are several irradiated pools outside of the gate as well as an intact army truck loaded with aqua pura crates.
The interior consists of a short stretch of intact tunnel filled with remnants of a recent Enclave occupation (turret, supply crates, etc.), now occupied by Brotherhood of Steel knights and scribes. One small service corridor on the southwest end connects the tunnel with the Capital Wasteland, while another on the northeast corner leads to the Satellite Relay Station. Seven sets of Enclave power armor can be found in the tunnel, on the bodies of dead Enclave soldiers, in a bus stop on the east side of the main chamber and lying among rocks along the west wall. In addition, several containers with random, valuable loot (a first aid box, 2 grenade boxes, 2 Enclave crates, and an unlocked safe) are also scattered around the Brotherhood of Steel staging area, and a room just off the entrance hallway holds 5 ammunition boxes.
Before the completion of Death From Above's final objective, the Brotherhood of Steel abandons the tunnel; leaving all equipment and supplies behind.
The tunnel cannot be accessed before Death From Above except by the use of console commands.
When you travel through here fighting the Enclave, you will go off the main map.
There is almost always a wandering hostile creature outside the gates near the irradiated pool and army truck (often deathclaws or albino radscorpions at higher levels). This is not normally a hazard as if you are on your way to complete Death From Above then you will be helped by nearby Brotherhood of Steel.
Once inside the tunnel itself, it has its own world map.
The Enclave soldiers' bodies never disappear, so they can be used for storage.