The construction of Castel Gandolfo is based on the ancient and splendid Roman villa of Albanum Domitian which was the residence that the emperor Domitian built between the years 81 and 96. The town remained in oblivion until 1200 when the Genoese family of the Gandolfo built the castle on top of the hill overlooking the lake. Even when the papal footprint was engraved in the middle of the 16th century, the reconstruction of the Papal Residence was designed by Carlo Maderno for Pope Urban VIII in the17th century, however, Pius XI later added the Papal Palace and the adjoining villa Barbarini. The small square in front of the Residence was renamed in 1870 with the name of Liberty Square during the movement for Italian unity. The Papal Palace was uninhabited from 1870 to 1929 when Mussolini, with the signature of the Lateran Treaty, recognized the Holy See as its owner.

Once lying amid vineyards, Grottaferrata is today one of the most elegant and popular residential areas and holiday locations in the Castelli Romani region. The small town is particularly known for the Abbazia di San Nilo (Abbey of Saint Nilus) around which the residential area developed throughout the centuries. Even nowadays, the Abbey is considered the town's landmark. The Abbey is home to the Basilian monks who follow the Byzantine rite observed by the Church of Constantinople. The monastery was founded 50 years before the Great Schism yet after this period remained in communion with the Church of Rome while preserving the Byzantine rite and monastic traditions. Therefore, any Catholic can take part in the Bizantine rite in the Abbey of Saint Nilus and can receive its sacraments. Grottaferrata is also renowned for its historical National Fair, which has taken place every year, in early spring, since the 11th century. This was at the time when a great number of pilgrims and merchants visited the Monastery periodically.

Frascati is famous for its villas built by the papal nobility from the 16th Century, to serve as lodging for the representative delegation and as summer vacation residences. These beautiful villas, built by the most prestigious architects and artists of the 16th and 17th centuries, are surrounded by cultivated land, forests and scenic gardens. Other rather well-known villas include Villa Aldobrandini, Villa Falconieri, Villa Torlonia, Villa Mercede, Villa Grazioli and Villa Mondragone.