Castelldefels Castle is perched on a hill at 59 metres above sea level. This monumental ensemble, which lends its name to the town, was built in the 10th century over what had been an Iberian settlement and, later, a Roman villa.

The castle was strategically constructed overlooking the Mediterranean Sea, overlooking a commanding position to control the territory and the coastal strip.

It was used for centuries as a fortress to defend the Eramprunyà barony, and was restored and fortified in the 16th century against attacks by Berber privateers.

Piracy began to fade away in the 18th century, and the castle fell into the hands of several noble families. One name that is closely associated with the fortification is the banker Manuel Girona, who bought and spearheaded the restoration of this iconic city landmark in 1897.

During the 20th century, it was used as a military training centre by the Republican authorities during the Civil War in 1937 and early 1938. Shortly afterwards, the castle and church were converted into a prison for international brigade members in March of the same year. Visitors can see original graffiti by these brigadiers in Santa Maria church in Castelldefels. This 10th-century church is the part of the ensemble that retains the oldest remains, with walls dating from the Iberian, Roman, medieval, modern and contemporary periods.

Both the castle and the church have been declared a Cultural Asset of National Interest.

Another impressive feature is the Fencing Room, which is decorated with 18th century paintings, and the Institutional Room, or the Noble Room, which bore witness to the grand feasts and celebrations attended by the Catalan bourgeoisie at the beginning of the 20th century, and which retains its neo-Gothic décor.