Church and Convent of San Bernardino de Siena is about 1 km (.6 mi.) s.w. of the main plaza via Mex. 180 to Calle 41A. The fortifications of this massive complex, built between 1552 and 1560 by the Franciscan Order, were meant to ward off the warring Mayas, who sacked it repeatedly. It was constructed next to a large cenote, with a paddle wheel over the opening providing fresh water.
A recent underwater excavation revealed weapons and munitions discarded during the War of the Castes in the mid-19th century; a large exhibit of these items along with photos of the excavation can be seen in the onsite museum. The church and chapels contain a number of religious artifacts.