How do you start fallout 3 the pitt?

Answer 1

When The Pitt first loads, the player will be informed of a new radio distress signal from a runaway slave named Werhner, who informs the Lone Wanderer that he needs help in retrieving a cure for mutagions plauging the town developed by The Pitt's raider boss, Ashur.

The signal emanates from the Radio tower far to the north of the Capital wasteland. It's a long walk from anywhere, but the closest map marker to fast travel to is Sat-Com ArrayNN-o3d. Once the player arrives, Wernher will be under attack by a few Pitt Raiders. After helping him dispatch his foes, Wernher will tell the player his story and where to go. He tells the player there is a Train Tunnelto the west, and he will meet up with him or her there.

This train tunnel is your entrance to the pitt, hope my answer helps =p