Castell de Montbui in Bigues i Riells dates to the 10th century and sits atop a hill at 541 meters elevation in the Vallès Oriental region of Catalonia. Originally part of the Hispanic March under the County of Barcelona and later serving as a prison for the Archbishopric of Barcelona, the castle's remnants include visible dungeons and courtroom facilities. Though largely ruined following the War of Succession, fragmentary walls and tower remains offer panoramic views across the Vallés region toward the Barcelona coast and Collserola tower, reflecting its strategic medieval importance.
