Gryffindor girls' staircase

"I wonder if Hermione’s seen this yet?” Harry said, looking around at the door to the girls’ dormitories. “Let’s go and tell her, said Ron. He bounded forward, pulled open the door, and set off up the spiral staircase. He was on the sixth stair when it happened. There was a loud, wailing, klaxonlike sound and the steps melted together to make a long, smooth stone slide. There was a brief moment when Ron tried to keep running, arms working madly like windmills, then he toppled over backward and shot down the newly created slide, coming to rest on his back at Harry’s feet. “Er — I don’t think we’re allowed in the girls’ dormitories,” said Harry"[...]"

- Harry and Ron attempting to ascend the staircase to the girls' dorms in Gryffindor house

This staircase was located in Gryffindor Tower which was accessible from the seventh floor of Hogwarts Castle. It led to the girls' dormitories.

History
Back in the era of the Hogwarts founders, a common belief was that girls were more trustworthy than boys, and as such, Godric Gryffindor enchanted the girls' staircase so as to turn into a slide should a boy set foot upon it. No such enchantment has been put in place to keep girls out of the boys dorm.

During the 1995–1996 school year, the staircase turned on Ron Weasley and Harry Potter, who had been trying enter the girls dormitory to contact Hermione Granger. The stairs turned into the magnificent slide, and Ron fell. Hermione herself came down moments later, following a pair of laughing girls.

Behind the scenes

 * The enchantment on the girls' staircase is possibly an extension of the spell, Glisseo, which was used by Hermione when being pursued by Death Eaters during the Battle of Hogwarts.
 * It is never stated if the enchantment on the staircase, or something similar, is in place on the entrances to the girls' dormitories in the other houses. It is highly likely though, as Hermione cites the founders collectively when explaining why boys can't enter the girls' dormitories but not the other way around.
 * In the film adaptation of Harry Potter and the Philosopher's Stone, after Harry, Ron and Hermione escape from Filch and Fluffy the Three Headed Dog, they are discussing the events of the night and all three of them walk up the staircase to the girls' dormitory. This error probably occurred because the film was made before the Order of the Phoenix book was written, and this is when the enchantment is first mentioned.

Appearances

 * Harry Potter and the Order of the Phoenix