Wikipedia
Piombi
Piombi (The Leads in English) is a former prison in the Doge's Palace in Venice. The name of the prison refers to its position directly under the roof of the palace, which was covered with slabs of lead. In winter, these slabs let the cold pass and they acted as a catalyst in the summer heat, imposing harsh conditions for inmates.
In 1756, Giacomo Casanova made a famous escape from the prison. He published the story of his escape in 1787.
The Old Prisons inside the Doge's Palace were supplemented by the New Prison, built across the Rio de Palazzo from the palace. The New Prison was connected to the Old Prisons in the Palace by the Bridge of Sighs.