The Papal Palace of Castel Gandolfo (or the Apostolic Palace; le palais des papes; Papstpalast ).Castel Gandolfo; this lakeside little town outside of Rome is the Popes'summer residence for 400 years.- The Papal Palace is a 55-ha complex of buildings in a garden setting in the city of Castel Gandolfo; Italy; including the principal 17th-century villa; an observatory and a farmhouse. The main structure; the Papal Palace; has been a museum since 2016. It served for centuries as a summer residence and vacation retreat for the pope.Castel Gandolfo; Italy. 2002.