The Gryffindor Boys' Dormitories are where the male Gryffindor students sleep and keep their possessions. The dormitories are accessible from the Gryffindor Common Room, which is located in Gryffindor Tower.
From the Story
"The Gryffindor boys' dormitories lead off from one of Gryffindor Tower's spiral staircases. Harry's dormitory is at the top."