This is where the common room is for the Slytherins, located in the dungeons and extending partway under the lake. The entrance is behind a wall in the cellars. Their common room is decorated with green lamps and chairs, and its atmosphere has been described as both grand and cold.

This is where the Potion Master's office is. They have their secret store of ingredients in here, as well as any potions they may be working on.

This is where all the students go to learn how to brew potions.