Milan, Italy, Castello Sforzesco - One of the largest citadels in Europe.

Originally a Visconti fortress, this iconic red-brick castle was later home to the mighty Sforza dynasty, who ruled Renaissance Milan. The castle's defences were designed by the multitalented da Vinci; Napoleon later drained the moat and removed the drawbridges. Today, it houses seven specialised museums, which gather together intriguing fragments of Milan’s cultural and civic history, including Michelangelo’s final work, the Rondanini Pietà, now housed in the frescoed hall of the castle's Ospedale Spagnolo (Spanish Hospital).