The Quad[1] (also known as the Paved Courtyard) is a courtyard located on the Hogwarts Castle exterior area. It is connected to the Viaduct and the Boathouse. Four towers are located at either corner of this courtyard: The Grand Staircase Tower, Gryffindor Tower, North Tower and Stone Bridge Tower; and the Hospital Tower and Suspension Bridge Towers are located in the middle of two different sides.

~taken directly from the Wikipedia page.