The Igreja Paroquial do Castelo, also known as the Church of Santa Cruz, is an 18th century building, occupying the site of the original temple built in the 12th century, where once stood an old mosque. It has a considerable religious, artistic and cultural collection and holds the oldest parish registers in the city, with the first marriage record dating back to 26 of September 1536.

According to tradition, it was a moorish mosque which, after the reconquest of Lisbon on 25 October 1147, was purified and consecrated by the Archbishop of Braga, João Peculiar, and four other suffragan bishops. This consecration took place on the 1st of November of the same year, for the royal procession led by King Afonso Henriques to enter, along with a relic of the Holy Cross, which is now on permanent display inside the church.

It is a single-nave church with three chapels on each side and respective tribunes in different artistic styles, namely Baroque, Pombaline and Neoclassical. It also has a bell tower that rests on the tower of the Alcáçova wall of St George's Castle, which is now used as a tourist attraction through the "Church Tower" project.

The Parish Church of the Castle is linked to the cult of St George - dedicating an altarpiece to him - the saint who defeated the enemies of the faith, patron saint of the reconquest of the city of Lisbon who, it seems, came along with the English that helped in the battle against the moors.

Although not on public display, the church also has nine paintings by Domingos António de Sequeira, a Portuguese painter from the second half of the 18th century, depicting members of the Carthusian Order in martyrdom.