St. Peter’s Basilica may be a pilgrimage site for Catholics, but even non-believers can appreciate the church’s architectural majesty. The original dates back to 349 A.D., when Constantine had a basilica built over the tomb of St. Peter, the first pope. That church was razed to make way for the current one, the world’s largest church at 18,000 square yards, which has been standing on this spot since 1626. Inside you’ll find Bernini’s masterful altarpiece—the great bronze baldacchino—and Michelangelo’s Pietà.