The Slytherin common room was located in the dungeons, and its entrance was hidden behind a stone wall that only opened when a specific password was spoken. Inside, the room was decorated in shades of green and silver, with elegant furniture befitting a group of students who so often form the wealthiest cohort at school.

The walls were covered in portraits of past Slytherins, and a large window looked out into the depths of the Black Lake, where students could sometimes see the giant squid passing by. Both the green hanging lamps and the dim light of the lake cast the room in a greenish light, giving the impression that the common room itself is underwater.