The frozen bubbles that form on the icy surface of this Canadian lake contain enough methane to create a small explosion.

An ancient knight and a symbol of the city's freedom.

When a supermarket opened up shop within a medieval building it became protected by UNESCO on a technicality.

A wonderfully strange collection of 500+ stuffed frogs doing people things.

A musical instrument played by the sea.

This building has two facades of clashing architectural designs.

Sofia's legislative center is continuously reinventing itself.

"Holy Wisdom" overlooks the city that became its namesake.

A vast Communist-era exhibition space in the Bulgarian capital.

A mountain pass in Bulgaria's Balkan Mountains was the site of four historic battles.

This ancient theater, restored in the 20th century, lives on as a venue for dramatic and musical performances.

A striking symbol of the Bulgarian capital.

The crypt of the imposing Stephensdom holds royal intestines and thousands of skeletons.

This deconsecrated church has seen many uses, from a tobacco storehouse to a cinema.

Two stone columns flank the grand Venice square, but there were supposed to be three.

Thousand-year-old Viking runes adorn an ancient Greek lion at the entrance to the Venetian Arsenal.

The marble facade hides a little-known medical museum with early surgical instruments and rare copies of canonical texts.

Those who own or stay at this 500-year-old, allegedly cursed house often meet terrible fates.

Go inside to really appreciate this 500-year-old technological masterpiece.

This palatial spiral staircase was so unusual the name "snail" was given to the noble family who built it.

This Venice bookstore has resigned itself to constant flooding by keeping its books in bathtubs and boats.

There was a top secret plan during World War II to seal a group of soldiers inside the rock.

An ancient and majestic fortress that played an integral role in Portugal's road to independence.

This unreal Portuguese palace looks as though it's made from a pile of different castles.