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.

There is an immense amount of loot available at Raven Rock including the rare Tesla Armor and Plasma Rifle so make sure to leave plenty of room in your inventory before you reach this area.

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.