Fallout 3/Project Impurity

Infect project purity's water supply. (Or not.) This quest activates once the final barrier to project purity is down.

At raven rock, you were given a vial of a modified FEV strain, which allegedly will cleanse the area from supermutants and other genetic impurities. However, you can instead give the vial to the Brotherhood of Steel for analysis.

Control room
At the control room, there are three options:
 * Do nothing and flee.
 * Convince Lyons to enter the control room.
 * Enter the control room yourself.

The combination to project purity is 2-1-6. You can learn this from the audio logs created by James, which point to the Book of Revelations, verse 21:6.

The radiation inside the control room is lethal. When using the Advanced Rad Suit and Rad-X, you will take approximatly 1 rad/second until you successfully enter the code - at that point, a cutscene takes over and kills the player.