Walking with Spirits

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

Walkthrough
You receive this quest from Desmond after defending Calvert Mansion from Tribals, Desmond asks you to infiltrate the Tribals to found out why the Tribals are attacking Calvert Mansion. You are directed to the Ark & Dove Cathedral and talk over the intercom with one of the Tribals. After convincing him you want to join, he will send you on a test. He tells you to find the mother of the Punga plants and take her giant seeds.

Once inside the bog, you will fight through several mirelurks. When you take the seeds of the plant a gas sprays out from the fruit and your character falls over. When you awake, you experience a psychedelic hallucination. In other words, you start TRIPPING BALLS! You will find giant bobbleheads with cryptic messages written on them. You will be attacked by ghost Ghouls (that won't hurt you), journey through an upside-down swamp, and even find the skeleton of your dead mother (with a nearby bobblehead explaining that it would have wanted to die with you as a kid). You will find several dead bodies of people from the Capital Wasteland, including Moira Brown and Elder Lyons, then find the Megaton bomb with a character similar to Mister Burke standing in front of it. The bomb explodes and you awaken in front of the Sacred Bog.

When you return to the Ark & Dove Cathedral, you are permitted entry. If you enter third-person, you will notice that any headwear you had equipped is presently gone, and you have a large scar on your forehead. You will be unable to equip the headwear you were wearing until you have the scar removed by...Nadine! Apparently, she has joined the Tribals to procure their Punga, in failing to achieve her original goal of discovering treasure in Point Lookout.

Reward
Access into the Tribal's headquarters.