The Slytherin common room is found in the dungeons of Hogwarts Castle, and is located underneath the Hogwarts Lake. Because of its location, the light in the common room is green. Harry Potter entered the common room in his second year to find out if Draco Malfoy was the one opening the Chamber of Secrets. The Slytherin Dungeon is located behind a wall in the cellars of Hogwarts School of Witchcraft and Wizardry. A password spoken to the wall is required to enter it; whereupon a passage is revealed leading to the common room -- a low-ceilinged, dungeon-like room with greenish lamps and chairs. This dungeon extends partway under the lake, giving the light in the room a green tinge. The common room has lots of low backed black and dark green leather sofas with buttons, skulls, and dark wood cupboards. It has quite a grand atmosphere, but also quite a cold one.