Half-Life Easter Egg - "Redrum"

Go to map c3a2f via the console (press the Tilde key and type "map c3a2f"). You should find yourself in a room with some steel crates, a map of the "reactor" tower, and a dead Science Team character laying in a pool of his own... um... blood.
If your peristalsis hasn't reversed, stand opposite the tower map and carefully inspect the bloodstain, remebering that Marc Laidlaw, writer of Half-Life's storyline, is a fan of Stephen King.
"247" is the number of the possessed hotel room in "The Shining", a novel written by Stephen King. But this egg doesn't end here; by travelling through "reactor" tower portals "2", "4", and "7", the player can escape the tower puzzle.