Ivy-covered Medieval tunnels cut through this charming town in France's Loire Valley.

Figures of unknown origin carved into the surfaces of underground caves.

Beautiful carved tunnels.

A sublime medieval path adorns the marble floor of one of the most beautiful Gothic cathedrals in France.

A centuries-old complex of hand-dug stone chambers has sheltered locals in times of trouble.

The somewhat misnamed 'Garden of Shells' lovingly built from found objects.

This is what trains will look like after the zombie apocalypse.

An underground city of ancient quarry tunnels hid thousands of Allied soldiers in WWI.

The tomb of a hard traveling saint is constantly covered in shoes as offerings to heal disabled youth.

This bunker in northern France was built by Nazi German forces with the intention of launching up to 50 V2 rockets at London each day.

Ancient paintings known as the "Sistine Chapel of Cave Art."

This impressive chasm is one of the longest natural underground cavities in the world.

A 14th century bridge built as a fortress, where the devil lurks on one of its towers.

These imposing walls and towers look more like the ruins of a fortress than a monastery.

This ancient Irish tower could easily have stood in for Rapunzel's prison.

Petrified footprints of one of the very first vertebrates to walk on land.

This natural sea arch highlights Ireland's rugged coastal beauty.

This 30-foot pile of rocks may be the grave of a mythological Irish queen.

At this cozy bar tucked down a hidden Galway backroad, Guinness makes the Gaelic come out.

A tribute to the incredible generosity the Choctaw Nation showed the Irish people during the Great Famine.

A stunning Victorian abbey and walled garden on a lakefront.

The world's toughest modern Christian pilgrimage leads directly to the gates of Hell.

This controversial Irish show cave is home to a massive formation known as the Great Stalactite.

The oldest pub in Ireland may also be the oldest surviving bar in the entire world.