Raven Rock

 is the Enclave's main base of operation in 2277. It can be found in the northwestern part of the Capital Wasteland. It is inaccessible until a portion of the main quest and depending on certain choices can become inaccessible afterwards. You arrive here after Finding the Garden of Eden and escape during The American Dream.

There is an immense amount of loot available at Raven Rock including rare Tesla Power Armor, Plasma Rifles, and AER9 Laser Rifles and Gatling Lasers. So before you leave Little Lamplight for Vault 87 make sure you only take the essentials as you'll find much more than you can carry, because after you leave it the door seals for good.

After leaving if you shoot in bunker's hatch using The Terrible Shotgun (possibliy normal shotgun would also work), outside hatch is blasted away. Perhaps there is way to unlock the second (internal) hatch and enter the bunker.

Apperances
 only appears in Fallout 3.

Behind the scenes
Raven Rock Mountain Complex is a real-world government complex that became operational in 1953.

Incidentally, a settlement of the same name also appeared in one of Bethesda's earlier games; the Morrowind expansion pack Bloodmoon.