This small, ancient Roman temple was once a church dedicated to the patron saint of penitents.

Natural sonic phenomenon comes with a grisly legend of murder and blood.

This spectacular track has run continuously since 1882.

No one knows exactly how deep the world’s deepest geothermal hot spring is.

This cathedral's stained-glass patchwork of psychedelic colors and shapes was put in place long before the swinging 60s.

Originally meant to hold a statue of King William IV, this support sat empty for years. Today, it hosts a rotating cast of public artwork.

Once seen as a bit of an eyesore, this sculpture has become a staple of downtown Houston.

Old ships and machinery fill a historic harbor in the city that's home to Europe's largest port.

These slanted cubic abodes are a creative if odd solution to a zoning pickle.

Housing the groundbreaking maps and globes of Gerard Mercator.

This narrow Ghent alleyway is an officially sanctioned street art tunnel.

This fairytale castle was built as a show of power but was nearly torn down thanks to its history of torture.

A rare example of World War I trenches from the British front.

This memorial museum chronicles the apocalyptic destruction of the First World War.

A moving memorial to the fallen and missing from WWI trenches.

In the shadow of a former battleground, the resting place for nearly 2,000 soldiers who died in World War I.

This triumphal arch celebrating the Sun King's conquest of Lille is a masterpiece of military architecture.

Tables of secondhand books fill the inner courtyard of this 17th-century stock exchange.

At Monet's beloved home you can still see the Japanese bridge, waterlilies, and weeping willows that were the subjects of some of his most iconic paintings.

His "Lionheart" is entombed separately from the rest of his body.

A memorial to the nearly 10,000 American soldiers laid to rest on the beaches of Normandy during WWII.

Remains of the artificial harbours invented for the Allied invasion of Normandy can still be seen at sea.

This enormous "cloth of the conquest" depicts the Norman invasion of England in mind-blowing detail.

This 1,300 year old monastery built atop a single rock was once only accessible depending on the whims of the tide.