The city's oldest church, San Ignacio de Loyola (St. Ignatius of Loyola), was built by the jesuits between 1686 and 1722, and forms part of the Manzana de las Luces.
The church is the work of the jesuit architects Krauss, Bianchi and Prímoli. It sits on top of a series of underground tunnels that were costructed during colonial times for defence and contraband.
After the expulsion of the jesuits from Spanish America in 1767, the church served as the city cathedral, and city's defending army holed up here during the British invasion of 1806.
Some interesting characteristics of the church, shared only with the Metropolitan Cathedral of Montevideo, are the dome built upon a quadrangular drum in the transept, and the double height of the side naves. The facade has a Bavarian baroque influence and the original 17th century main altar was carved from wood and later gilded by Isidro Lorea.