Not castles but small towns
The castelli, which are not castles but small towns, lie between Rome’s old road (Via Appia) and her new (Autostrada del Sole). They are draped on the shoulders of the volcanic Alban hills around the crater lakes of Albano and Nemi. Frascati, only 25 minutes in the suburban train from Rome Termini station, is synonymous with refined dry white wines. Well-preserved houses in woodland and shady avenues named for twinned towns (including Maidenhead in England) are ranged on a 300-m balcony of the hills overlooking Rome. Spacious villas (parks) of the cardinal princes and Roman nobles cluster round Frascati. Villa Aldobrandini is rich in statuary, fountains and grottoes. Bus excursions to classical Tuscolo.
Best-known of the castelli is Castel Gandolfo, perched on the rim of Lake Albano. A narrow street ascends to the Pope’s summer palace, past a fountain by Bernini (in Piazza del Plebiscito). With a permit from the Prefettura della Casa Pontifica, Vatican City, you may visit Villa Barberini, the papal observatory. Funicular railways shuttle back and forth to the lake and on the streets you run a gauntlet of sacred memento stalls and their vociferous owners. Castle Gandolfo always has a holiday air.
A one-day tour: leave the autostrada at San Cesareo, follow Route 216 to Grottaferrata (frescos and catacombs), 297 to Castle Gandolfo and Albano Laziale (Roman gate, tombs and amphitheatre), 7 to Genzano (views), north on minor lakeside road to Ariccia and Nemi, 217 ‘Via Laghi’ to Rocca di Papa and its airy bluff (funicular in three minutes from Valle Violata), 218 to Frascati.