An underground tunnel network long rumored thanks to drawings by Leonardo da Vinci under Milan’s Sforza Castle are proven to exist. Ground-penetrating radar and laser scanning revealed that the historic passages made famous by a Leonardo da Vinci drawing is just one of multiple tunnel sections.

A technological investigation at Sforza Castle found that it does in fact hold underground passages once described by Leonardo da Vinci.

There's a hidden drawing underneath the "Mona Lisa" — and it shows that this masterpiece almost looked very different.

Italy’s famed Sforza Castle is a focal point for historians, architects, and art lovers—as well as a source of many legends. One of the most prominent rumors surrounding the over 575-year-old fortress has long been the existence of secret passageways beneath the grounds originally hinted at by Leonardo da Vinci.