A Common Room is The shared area for students to spend time with other members of their house. Protected by a portrait that requires a password, or in Ravenclaw’s case, an answered riddle.
Common Room History
The four houses of Hogwarts School of Witchcraft and Wizardry each have their own common room at the school, which is where they spend time free time. In general, the location of the common rooms are known only to those who are members of the house, though on occasion some exceptions have been made. The general area of each common room was fairly common knowledge, with Gryffindor and Ravenclaw each being located in two of the towers, the Slytherin common room being in the dungeons, and the Hufflepuff common room being located in the basement. According to the covenants of Hogwarts, it is not permissible for parents or professors to enter the common rooms without permission, likely from the Headmaster.