The village of Castel Gandolfo is an easy day trip from Rome. It is a hill town with a scenic lakeside location in the Castelli Romani region. It has a magnificent palace and gardens and a historic town centre. And it has an added quirk: part of Castel Gandolfo is outside of Italy, a part of the Vatican State.
Castel Gandolfo And The Castelli Romani
Castel Gandolfo is one of the Castelli Romani (“Roman Castles”). These are a group of hill towns to the south east of Rome, in a region formed by volcanic craters, with hills and lakes. It is a major wine-producing area. It is now a regional park, the Parco Regionale dei Castelli Romani.
Since Roman times the Castelli Romani have been popular with emperors, rulers and other wealthy individuals looking for a pleasant place to build their summer residences, away from the heat of Rome. The custom has continued, and even today the area is full of villas and holiday residences. (You can see a similar tradition at Tivoli, on the other side of Rome.)

What To See And Do In Castel Gandolfo
Castel Gandolfo is at the top of a hill overlooking Lake Albano. The town was a summer residence for the popes from the 17th century until recent times. The Papal Palace is under the jurisdiction of the Vatican City, and this part of the town is technically not a part of Italy.

For visitors The Papal Palace and Gardens are the main attraction. However, there is also an attractive historic centre, and lakeside activities.
Apostolic Palace And The Barberini Gardens
The Papal Palace is a complex of buildings with extensive gardens, built on the site of a villa once owned by the Roman emperor Domitian. The current pope, Pope Francis, opened the gardens to the public for the first time in 2014. Two years later he stopped using the palace as a residence, and it opened as a museum.

The Palace itself is full of opulent rooms. There are exhibition areas, and lots of portraits of former popes. The Renaissance style Barberini Gardens feature formal flower gardens, mazes, sculptures and fountains. There are also archaeological remains within the grounds, including a Roman amphitheatre.

Note that you will need to buy separate tickets for the Palace and the Gardens, and that it is advisable to check opening times in advance. As the property is part of the Holy See modest dress is necessary (shoulders and knees must be covered).
Historic Centre And Lake Albano
The town is based around Piazza della Libertà, the main square. Here you will find restaurants and cafés, some with terraces offering panoramic views. Elsewhere you can wander around the narrow streets and smaller squares, catching an occasional glimpse of the lake far below.

When you have finished exploring the town head down the hill to Lake Albano. Boat tours and water sports are available, and there is a further selection of bars and restaurants.

How To Get To Castel Gandolfo From Rome
The easiest way to get to Castel Gandolfo from Rome is to take a train from Roma Termini. The journey takes around 40 minutes. Note that the station at Castel Gandolfo is about halfway up the hill, so you will need to do a bit of climbing to get up to the town or down to the lake.
Guided tours from Rome are also available. On Saturdays you can take a tour via the Vatican railway, a train that departs from the railway station within the Vatican City itself. If you are already in Castel Gandolfo you could take a guided tour of the gardens and palace.
For those that have the time and the energy it is actually possible to walk to Castel Gandolfo from Rome! The town is on the Via Francigena, an ancient pilgrim trail, 28 km from the Vatican City.