Villa d'Este, Tivoli

Water is the true architect at Villa d'Este in Tivoli. Cardinal Ippolito d'Este channelled the river Aniene through a hillside garden in the 16th century, powering hundreds of fountains, cascades and jets — including an organ fountain that plays by hydraulic pressure alone. The estate set the pattern for grand European gardens for generations, and UNESCO added palace and garden to the World Heritage List in 2001 as the definitive Italian Renaissance garden.