Walking with Spirits

 is a Fallout 3 quest and achievement that is added to the game with the Point Lookout add-on. It is assumed that you will have to shave your head sometime during the add-on. Some time into this quest you will be drugged and you will halucinate and start seeing giant bobble heads. When the halucination is over you wake up with your head shaved and you will figure out that the tribals took part of your brain.

Walkthrough
You receive this quest from Desmond after defending Calvert Mansion from Tribals, Desmond asks you to infiltrate the Tribals to stop the attacks on the mansion. You must then find the Cathedral and talk over the intercom to a tribal so that you can gain enterance to the cathedral. So they send you in to see the mother of the punga plants and take the seeds. After you take the seeds and start to walk back it will look like your tripping on major drugs because people you know begin surfacing from the bog and then at the end you should see the megaton bomb and a man standing there. Then you wake up after the bomb explodes and are given the achievement. As a correction to the description the Tribals don't take part of your brain but it is actually the ferryman you met in the beginning of point lookout, you can later reattain you missing chunk of brain after the ferryman is locked up.