The Benedictine Monastery of San Nicolo la Rena is one of the largest monastic complexes in Europe and a UNESCO World Heritage Site, now part of the University of Catania. Rebuilt in Baroque style after the 1693 earthquake and Etnas lava flows, it features grand cloisters, frescoed halls and archaeological remains beneath. Ticketed guided tours explore its architecture, history and the layers of the city built over centuries on this site.