When the bus that transported Lazar and others from the Groom Lake facility reached Papoose Lake or S4, it made a sharp left turn after it passed the hangar doors to its left.

Once stopped, the bus door opened out to another steel door inset in the side of the mountain. The "workers" would step out, past guards holding barking snarling dogs. Except these dogs were different.  For all the fangs and snarling and barking, there was no sound coming out.  The dogs had their vocal chords cut out to avoid being detected.

Once inside the door, there was a single guard sitting at a desk in a barren room. Behind him was a door. The entrants were checked and led to another small room with a handreader and another door. This door led into the long hallway which ran the length of the hangar doors and also led to the briefing rooms, restroom and nurse's station. The white areas are the only areas Lazar was allowed to cover. And even then under guard.