Secret tunnels likely once drawn by Leonardo da Vinci discovered underneath a medieval Italian castle

Once only indicated through a sketch by Leonardo da Vinci from around 1495, concealed passageways have been discovered underneath the Sforza Castle in Milan, Italy.

​ Once only indicated through a sketch by Leonardo da Vinci from around 1495, concealed passageways have been discovered underneath the Sforza Castle in Milan, Italy. Read More Breaking News, Latest News and Videos | CNN