Fodor's Expert Review Castello di Giulio II
The distinctive castle, easily spotted as you come off the footbridge from the train station and part of the medieval borgo (old town), was built in 1483 by the future Pope Julius II when he was the cardinal bishop of Ostia. The structure's triangular form is unusual for military architecture, but it was strategically placed for defense when the Tiber River still flowed below its walls. After crossing a drawbridge to gain access the castle's interior, you'll find a small exhibit of historical sketches on the second floor.