Neemrana Fort Palace, Rajasthan, India

This list kicks off with a wildcard entry - this is a 10-story, 15th Century fort-palace located in the Indian state of Rajasthan. Spread over three acres, this beautiful hotel is built in a horseshoe shape into a hillside on the Delhi-Jaipur highway. The Aravalli mountain range can be seen from the hotel.
Pousada de Óbidos, Obidos, Portugal

Lying within the city walls of Obidos, this castle is now one of Portugal's finest hotels. Think well ahead if you're planning on staying here though - the hotel only has nine rooms, including one in the tower pictured above.
Swinton Park, Yorkshire, England

Swinton Park is an ancestral home that has been transformed into a castle hotel. It's complete with turrets, long, echoing corridors and grand staircases. All the rooms are individually decorated so you can enjoy fine English country living tailored to your needs.