The Swabian Castle stands at the northwestern corner of the old town, a muscular Norman-Swabian fortress originally built around 1132 and thoroughly remodelled by the Emperor Frederick II of Hohenstaufen in the 13th century. The trapezoidal plan with round towers at the corners is characteristic of Frederician castle design, the same architectural intelligence that produced Castel del Monte and Castel Maniace.
Inside, the castle houses plaster casts of architectural elements from across Puglia — a study collection assembled in the 20th century that serves as a catalogue of regional medieval carving. The views from the ramparts over the harbour, the old town and the Basilica di San Nicola are worth the climb. Temporary exhibitions of contemporary art are regularly hosted in the castle's main halls.