Beneath the southern end of the Golden Gate Bridge is the “Gibraltar of the West Coast,” a fort built to protect the San Francisco Bay from naval attack.

A mesmerizing landscape of 18th-century cellars carved out of the land.

A quiet memorial to those who died saving others in the heart of the City of London.

The ruins of a church destroyed by both the Great Fire of London and the Blitz, now turned into a peaceful garden.

A mysterious carving from 17th-century London seemingly depicts a young boy sitting on a bread basket.

A vast overgrown cemetery, once known as one of London's "Magnificent Seven."

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

The first geometric self-supporting spiral stairs in Britain are a truly beautiful sight.

This skeleton-filled altar piece served as a backdrop to one of the most iconic scenes in "The Sound of Music."

The world's newest astronomical clock is also its most accurate.

A perfectly preserved hill village where the buildings are painted like white lace.

Inside the Šomoška National Nature Reserve exists a unique rock formation rarely seen in the world.

Budapest's Communist-era statues, banished to the suburbs.

Oriental bazaar in the heart of Sarajevo.

Inat Kuća, or "House of Spite," is more than just an oddly named restaurant.

There's a mini version of Iguazu Falls hidden in the Balkans, and it's got a rope swing.

A field filled with carved medieval tombstones called stećak.

A futuristic, brutalist masterpiece that is also strangely prison-like.

Artists made this mosque into a marvel of Ottoman baroque architecture.

Depending on the region's rainfall, this church may be partially submerged.

A medieval bridge stretches over a sulfur-rich river that leads to year-round natural hot springs.

Since ancient times these picturesque springs have been providing bathers with healing waters.

Concrete strongholds stand guard over the Golden Gate.

A man-made island in scenic San Francisco Bay.