The Uffizi Gallery oversees the passage and it can only be visited on small group tours offered by private operators such as Context Travel.

BBC: Florence��s best-kept secret

Since the property is near Florence, singles can take in the historic sights in the city like the Uffizi Gallery and the Duomo on their downtime.

FORBES: Top Trips For Singles

Supporters of the Mafia theory note that it has been blamed for the burning down of the Petruzzelli theatre in Bari in 1991 and the bombing of the Uffizi art gallery in Florence in 1993.

ECONOMIST: The great Fenice mystery