The Iglesia San Pedro y San Pablo Apóstol stands in the centre of Caluco town as ruins. Construction began between 1525 and 1574 by Dominican friars — making it one of the oldest Catholic church sites in El Salvador. The Santa Marta earthquake swarm of July 29, 1773 (the same sequence that levelled Antigua Guatemala) destroyed it. The walls and arches remain.
Caluco was a Pipil-Nahua settlement that became one of colonial Central America's wealthiest cocoa-producing centres in the 16th century — the wealth funded this scale of construction. Today the modern church San Lucas Evangelista (1803) sits beside the ruins.
Open-air, no entry fee, no fixed hours. CONCULTURA-protected national cultural heritage. About 5 minutes from Thermal Paradise — worth a 30-minute walk-through on the way to or from town.