Cathedral Basilica of the Immaculate Conception in Castries, Roman Catholic minor basilica in Castries, Saint Lucia.

The Cathedral Basilica of the Immaculate Conception stands in central Castries where Peynier, Micoud and Laborie Streets meet, facing Derek Walcott Square. Completed in 1897 to Father Scoles's design, it measures 200 feet by 100 feet, the largest church in the Caribbean. Its wooden roof shelters a multicoloured interior painted by Dunstan St. Omer, with a Black Madonna and Child and Saint Lucy above the altar.

Plans to build this church began in 1807, but financial struggles delayed the project for decades. The current structure was founded in 1894 and designed by Father Ignatius Scoles, who employed methods to make it resistant to the tropical climate.

The interior was painted by Saint Lucian artist Dunstan St. Omer in multicoloured tones of bright red, green and yellow, with Caribbean and African influences. Above the altar stands Saint Lucy, patron saint of the island, and the decoration includes a Black Madonna and child. Marble plaques on the walls commemorate the dead, among them Bishop Charles Gachet, first bishop of the Castries diocese.

The church sits across from Derek Walcott Square in downtown Castries and is easy to reach on foot. Visitors should wear respectful clothing and check local worship times before entering if planning a visit outside regular tourism hours.

The cathedral holds the title of largest church in the Caribbean, measuring 200 feet (61 m) long by 100 feet (30 m) wide. It was raised to the rank of Minor Basilica on 11 May 1999 during its centenary celebrations. Pope John Paul II visited on 7 July 1986.