The boathouse is an underground harbour where the boats are stored. These are the same boats that are docked when the first years arrive to Hogwarts on 1 September every year. Up until 1995, there was a portrait of Percival Pratt hung on one of the inside walls of this boathouse. The portrait concealed a secret entrance to the Grand Staircase. Some small wooden boats are stored in the rafters of the ceiling.
After Pratt's portrait was taken away, there were only three entrances to the boathouse. The path outside (The Quad), the stairs that led from the Entrance Courtyard and the Lake.
Fireworks are occasionally set off from the boathouse exterior to signal a party.