The Chamber of Secrets is a legendary secret room constructed by Salazar Slytherin to house a monster which would finish his "noble work." This noble work would be accomplished when his true heir would open the Chamber and release the monster which lived within to rid the school of non-pureblood students.

According to the legend, Slytherin and Gryffindor argued over whether to allow Muggle-born students into Hogwarts. When Gryffindor apparently won, Slytherin left the school, but not before building the Chamber. Over the centuries, many great witches and wizards have searched for the Chamber but none found it. Eventually, the whole thing was assumed to be purely fiction. Until it was opened.

The Chamber itself is a huge temple-like room with pillars and carved serpents. There is a massive statue of Salazar Slytherin at the far end from which the basilisk comes when summoned. Now that the Basilisk has been defeated, the remains of the Chamber remain along with what was left of the monster. It has been deemed out of bounds by the Headmistress.