This is the largest and spookiest church in Sicily, stretching for 105m (344 ft.) with transepts measuring 42m (138 ft.). The cupola is 62m (203 ft.) high. Begun in 1687 by Giovanni Battista Contini, it was reconstructed in 1735 by Francesco Battaglia. Stefano Ittar designed the dome; the facade, with its mammoth columns, was left unfinished in 1796 but remains impressive. The interior is rather bare-bones. A beautiful 18th-century organ with 2,916 pipes is found behind the main altar. A meridian line was laid in the transept floor in 1841 to catch the sunlight precisely at noon. But because of the shifting volcanic land, today it catches the sun at 12:13pm. Sadly, the church will never be completed. Sporadic renovations try to keep it propped up, but the efforts seem doomed to failure.

The adjoining Monastero di San Nicolò all'Arena is the second-largest monastery in Europe, rivaled only by Mafra, outside Lisbon. This old Benedictine complex, dating from 1703, is now part of the University of Catania. Guided tours are available.