Lake Bolsena (Lago di Bolsena) is a crater lake in central Italy, of volcanic origin near the town of Bolsena. There are two islands in the southern part of the lake which formed by underwater eruptions following the collapse that created the caldera.
John Evelyn describes the Lake of Bolsena as:
“After a little riding, we descended toward the Lake of Bolsena, which being above twenty miles in circuit, yields from hence a most incomparable prospect. Near the middle of it are two small islands, in one of which is a convent of melancholy Capuchins, where those of the Farnesian family are interred. Pliny calls it Tarquiniensis Lacus, and talks of divers floating islands about it, but they did not appear to us. The lake is environed with mountains, at one of whose sides we passed toward the town Bolsena, anciently Volsinium, famous in those times, as is testified by divers rare sculptures in the court of St. Christiana’s church, the urn, altar, and jasper columns.”