Known as the mother of all churches, the Basilica of St. John Lateran is the seat of the bishop of Rome, a.k.a. the pope. Though slightly less grandiose than St. Peter’s, the Lateran is a masterpiece, known for its massive stacked portico facade designed by Alessandro Galilei. A line of apostles runs the 230-foot length of the church, while a 13th-century mosaic decorates the apse—there’s even a fresco fragment by Giotto. The Lateran’s best-kept secret? The 13th-century side cloister. For a few euro in spare change, the cloister, its unique spiral columns, and the cosmatesque mosaics are all yours.