The island where Emperor Augustus banished his daughter Julia, when he thought she had become too friendly with the men on the mainland. Incidentally, this same island became a military base during WWII for a 115-man German garrison deployed to defend a radar station. These were cunningly outmanoeuvred by a small group of American paratroopers, without a single shot fired.
East of Ventotene is the island of Santo Stefano. Santo Stefano has another large building, a prison, in use from 1795 to 1965.