Tivoli sits in the hills about 30 kilometres east of Rome and has been a retreat from the capital's heat and noise since antiquity. The Emperor Hadrian built his enormous villa complex here; Renaissance cardinals followed with the Villa d'Este and its famous water gardens. The town itself is pleasant enough, perched on a ridge above the Aniene river, but the villas are why you come.
Three sites make Tivoli worth a day trip. Villa Adriana (Hadrian's Villa) is a sprawling archaeological park — less a villa than a private city, with bath complexes, theatres, pools and palaces in a beautiful state of overgrown decay. Villa d'Este is a Renaissance palace whose terraced gardens are a masterwork of hydraulic engineering, with hundreds of fountains cascading down the hillside. Villa Gregoriana is a wilder affair — a steep park built around the dramatic waterfalls of the Aniene.
Tivoli is easily reached from Rome by regional train (about an hour from Roma Tiburtina) or by the COTRAL bus from Ponte Mammolo metro station.