The Third Floor Corridor on the right hand side was out of bounds during the 1991–1992 school year at Hogwarts because it was the access point to the Chambers where the Philosopher's Stone was being hidden. Fluffy, a three-headed dog owned by Rubeus Hagrid, guarded a trap door that led into the Chambers. Towards the end of the school term, Professor Quirrell gained access to the trap door by enchanting a harp to play music which lulled Fluffy into a state of sleep.
