The patron of Castel Gandolfo is Saint Sebastian: his patronal feast is celebrated on the first weekend of September, even though the saint's liturgical feast day falls on 20 January.
On 29 August 2026, marking the 400th anniversary of the start of papal stays in Castel Gandolfo, a pope took part for the first time in the traditional Madonna del Lago procession: Pope Leo XIV boarded onto the waters of Lake Albano. The hamlet of San Paolo, part of the municipality, instead celebrates Mary Help of Christians on the last Sunday. The town also holds the Collegiate Church of San Tommaso and the Palazzo Pontificio.
