Draco goes into the Room of Requirement several times in Harry Potter and the Half-Blood Prince. He learns about it from Harry and the Dumbledore's Army as they used it for meeting, and Draco was a major part of the Inquisitorial Squad that caught them. However, he uses it to repair a particular Vanishing Cabinet that has a twin in Borgin and Burkes. He finally repairs it and uses it to smuggle Death Eaters into Hogwarts.