Want to Explore Leonardo’s Subterranean Secrets?

Who could have guessed Leonardo da Vinci left secrets underground?

Me, that’s who. First, here’s what really happened.

Reality Sforza Castle, photographed by Jakub Halun, CC BY-SA 4.0, via Wikimedia Commons

In the 1490s, the duke of Milan, Ludovico Sforza, hired Leonardo to decorate Sforza Castle with artwork, and he complied. Since then, and down through the centuries, rumors persisted of hidden underground passages, secret corridors running beneath the castle.

Leonardo documented...