A large grotto built in the 16th century amidst Florence's famous Boboli gardens.

The doodles of a genius line the walls of a secret room under the Medici Chapel, where they were hidden for nearly 500 years.

A secret door leads to this cozy dive that sells only “milk.”

Hidden on a cobblestone street in Glasgow, a Czech Cajovna-inspired teahouse serves as a hangout for Bohemians.

A scattered trail of street art adds a pop of color to the city's stark structures.

This military tunnel dates back to World War II and provides visitors with a little wartime adrenaline.

Now abandoned, the world's first torpedo factory is crumbling into the sea.

This picturesque medieval monastery guards a small trove of historic treasures.

Humble beginnings for one of the world's most famous scientists.

Legend has it fairies gathered at the site of this medieval castle.

The remains of a sunken military ship wreck visible through clear water.

Yugoslavia's biggest underground airport lies in ruins.

A musical instrument played by the sea.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

An ethereal glowing blue ocean cave in Croatia.