Castelo de Silves
With high red walls that overshadow the little whitewashed houses below, this polygonal sandstone fortress was built between the 8th and 13th centuries and survived untouched until the Christian sieges. You can walk around inside the remaining walls or clamber about the crenellated battlements, taking in bird's-eye views of Silves and the surrounding hills. Its gardens are watched over by a statue of King Dom Sancho I, and its capacious water cistern is now a gallery space devoted to temporary exhibitions.