raven rock entrance

Well, if you already left Raven Rock when getting captured, you can't get back in.

If you haven't been in Raven Rock yet, play the storyline. Before getting the G.E.C.K, empty all of your inventory except a weapon and light armor. Get as much Armor and Weapons as you can in Raven Rock for lots of caps. Get the ZAT Self-distruct code in Coernal(spelling) Autumn's office, plus the Energy Weapons Bobblehead. When meeting the President, if you have a high enough science, he will kill himself, or use the code. I suggest the code.

After you leave, you can't get back in Raven Rock. Enjoy the Fireworks if you blow Raven Rock up. Stand back also.

Go through the Story line. Eventually, you'll get to the quest, "Finding the Garden of Eden". At the end of it, the Enclave will capture you and take you to their base. Make sure to do everything you want to do before leaving (Such as collecting weapons, ammo, armor, and the Energy Weapons Bobblehead to increase Energy Weapons by 10.) because once you leave, you ain't going back.

The reason you can't get into raven rock is because it is only opened during the main story line. Afetr you have completed the searching for the garden of eden quest than you awake in raven rock in a holding cell. After you talk to their commanding officer and done a talk sequence with him you talk to president eden and then you have to go to his office(grab the bobble head or it is lost forever) and get the virus from him then you go to the citidel(talk the president into blowing up raven rock.