Numerous secret passages have been discovered under Milan’s Sforza Castle, some of which were immortalised in drawings by Leonardo da Vinci.

Built in the 15th century, Sforza Castle has been extensively renovated and rebuilt over the centuries, earning it the title of one of the largest citadels in Europe. Today it houses several of the city’s museums and art collections.

Suspicions about secret passageways date as far back as the 1490s when it was thought that the Duke of Milan, Ludovico Sforza – or il Moro – had a tunnel built to reach the nearby Basilica di Santa Maria delle Grazie, where his wife Beatrice d’Este was buried following her death in childbirth.

Leonardo da Vinci, who was employed by the duke to decorate some of the castle’s rooms, had created drawings of this passageway and others thought to have been built for use by the military in case of attack.

The existence of these passageways has long been the subject of legends and speculations. However, with the use of technology...