Much of northern Spain belongs to Castile-Leon, an autonomous region surrounded by mountains. Architectural gems like the Romanesque stonework of Segovia's city walls, the Gothic Burgos Cathedral and the dramatic Baroque square in Salamanca are complemented by the area's natural beauty. Parque Natural de las Hoces del Rio Duraton is marked with deep gorges and shelters many birds of prey, while Parque Natural del Lago de Sanabria y alrededores contains the largest glacier lagoon on the Iberian Peninsula.