Walking with Spirits

 is a Fallout 3 quest and achievement that is added to the game with the Point Lookout add-on.

You receive this quest from Desmond after defending Calvert Mansion from Tribals, Desmond asks you to infiltrate the Tribals to stop the attacks on Calvert Mansion. You must then find the Ark & Dove Cathedral and talk over the intercom with 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. When you take the seeds  a gas sprays out from the fruit and your character falls over. But you're not hurt so start to walk back. Ghouls that aren't really there attack you, Nuka-Cola Quantum bottles fall out of the sky and explode, and Pip-Boy Bobbleheads show up. None of these illusions can harm you. People from the Wastes begin surfacing from the bog, you see your Mother and soon, the Megaton Bomb and Mr. Burke leaning on it. Then you wake up from the effects of the seeds.

Reward
Access into the Tribal's headquarters.