The Gryffindor common room is located in one of the castle's highest towers, the entrance to which is located on the seventh floor in the east wing of the castle and is guarded by a painting of The Fat Lady, who is garbed in a pink dress. She permits entry only after being given the correct password.
Ravenclaw Common Room
The dormitories are located in Ravenclaw Tower, on the west side of Hogwarts. The common room, is round and filled with blue hangings and armchairs, has a domed ceiling painted with stars and features a replica statue of Rowena wearing her diadem. Also keep in mind that Ravenclaws "have a spectacular view of the surrounding mountains". A logical riddle must be solved to gain entry, whereas the Gryffindor and Slytherin common rooms only require a password, indicating that it may be easier for those students from other houses who possess a high degree of intelligence to enter this common room than others.
Hufflepuff Common Room
The Hufflepuff dormitories and common room entrance is “ concealed in a stack of large barrels in a nook on the right hand side of the kitchen corridor.” To enter, one must tap the barrel two from the bottom in the middle of the second row in the rhythm of 'Helga Hufflepuff'. Unlike any other house, the Hufflepuff common room has a repelling device that douses the illegal entrant in vinegar if the wrong lid is tapped or the rhythm is wrong. The Hufflepuff common room is filled with yellow hangings and fat armchairs and it has little underground tunnels leading to the dormitories, all of which have perfectly round doors, like barrel tops (much like a badger sett).
Slytherin Common Room
The Slytherin dormitories and common room are reached through a bare stone wall in the dungeons. The Slytherin common room is a long, low, dungeon-style room, located under the Hogwarts Lake, furnished with green lamps and carved armchairs. The room is described as having a greenish glow.