The existing Church of Sant’Antonio Abate was enlarged between 1597 and 1606 following the transfer of the Episcopal See to Castelsardo, when the church was given the title of Cathedral.

The interior is predominantly Gothic, but it underwent numerous remodeling projects that changed its original appearance. Different styles coexist in the building; the 17th-century works in particular gave the building its single-nave structure, with lowered barrel vaults and side chapels on buttresses, while the apse is quadrangular with a cross vault. 

The building was completed in 1727 with the construction of the women’s gallery and the finely decorated altar dedicated to Sant’Antonio Abate, patron saint of the town, at the head of the transept. The bell tower was not constructed but formed directly from a tower of the ancient walls, originally a lighthouse, the dome of which was subsequently covered with polychromatic tiles.

Stands out from the main altar the Madonna Enthroned with Child of the anonymous sixteenth-century Master of Castelsardo. This board completed a dismembered altarpiece of which other surviving parts are in the Diocesan Museum, housed in the crypt of the Cathedral.

The spaces are enriched with wooden furnishings, Baroque-style altars and statues dating to the 17th-18th centuries. One of the finest side chapels is dedicated to San Filippo Neri, with carvings and polychromatic decorations. The Chapel of the Virgin has small octagonal domes and the walls are covered with azulejos, the majolica tiles of Arab-Spanish culture.
Above the entrance stands the lovely 18th-century pipe organ, considered to be one of the most beautiful in Sardinia. Also worthy of note are the wooden pulpit and the carved stalls of the choir created by Jaume Camilla in 1765.