Four Seasons Istanbul Sultanahmet, Turkey
This stunning, neo-classical building might well be one of Turkey's more luxurious places to stay but it wasn't always that way. Built in 1918, the prison was mainly used to imprison communist leaders and the writers, journalists and intellectuals who supported them during the 20th century. However, since 1996 it's been a luxury hotel. Gleaming elevators now swoosh up and down what were once the watchtowers of this converted prison, while the exercise yard is now a surprisingly stunning outdoor dining area.