The main entrance is chained so you have to go around to the west side of the building. You'll find the dismembered body of Private Hart. Loot his body to start the quest “The Devil's Due”.
There will be constant shaking and you'll immediately feel you've stepped in something out of a horror movie. Continue moving along the basement and loot any containers and bodies you'll find. Continue upstairs and carefully walk around. You'll have to fight a very high-leveled Deathclaw so it will be a good idea to lay down traps in advance. Or, if you're really confident, just launch two mini-nukes at it (from a safe distance of course)
Notable Loots: