The Chamber of Secrets is a legendary secret room constructed by Salazar Slytherin, one of the four Hogwarts Founders, without the knowledge of his colleagues Godric Gryffindor, Rowena Ravenclaw, and Helga Hufflepuff. The chamber's creation stemmed from a fundamental disagreement over student admissions; Slytherin believed that magical education should be reserved for those of pure-blood lineage only, excluding Muggle-born students. When his views were rejected, he left the school, but not before secretly building the Chamber. According to legend, Slytherin sealed a monster within the Chamber—a Basilisk—that only his own true Heir of Slytherin could control. The purpose of the Chamber and its monster was to one day purge the school of all who were, in Slytherin's view, unworthy to study magic. For centuries, the Chamber was considered a mere myth. The entrance is located in the second-floor girls' lavatory, the one haunted by Myrtle Warren (Moaning Myrtle). One of the copper taps, which has never worked, is marked with a tiny, scratched snake. Speaking the Parseltongue word for “Open” causes the sink to vanish, revealing a large, dark pipe. This pipe is a slide that leads into a series of stone tunnels far below the school, littered with the skeletons of small animals. The main tunnel terminates at a solid wall, upon which two intertwining stone serpents are carved. Again, Parseltongue is required to make the wall open into the Chamber proper. The Chamber itself is a long, high room filled with a greenish, dim light. Tall stone pillars carved with more serpents rise to a ceiling lost in darkness. At the far end of the Chamber stands a colossal, ancient-looking statue of Salazar Slytherin, which serves as the lair for the Basilisk.
The Chamber is central to the plot of Harry Potter and the Chamber of Secrets and plays a significant role in the final book.