Some of England's last cave dwellers lived and worked within this huge cave.

The whimsical twist of this spire was either caused by the Devil, an unexpected virgin, or lead.

Inspired by a dream, a hermit carved out a home in this sandstone bank to live a life of contemplation and prayer.

A 16th-century horror show built in a lovely Italian garden.

An Italian crevasse filled with abandoned buildings gives visitors a look at the world without humans.

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

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

The world's largest reflecting pool is just two centimeters deep.

Beautiful carved tunnels.

A public park off the beaten path with a beautiful waterfall and 13th century Cistercian abbey.

This ancient Roman bridge and aqueduct still stands as a wonder of classical construction.

The famous winding walk at Chartres is surrounded in mystery and myth.

A French valley with forests so lush it was nicknamed "the Small Amazonia of the Pyrenees."

The largest underground church in Europe.

This natural French spring has been turned into a magical grotto by Roman and medieval constructions.

A cave dwelling that was started by the Celts, expanded by monks, and finished by knights.

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

Twelve grave-faced marble angels guard the emperor's tomb at Les Invalides.

Sacked by Vikings, blessed by William the Conqueror, dealt a fatal blow during the French Revolution—these ruins have seen it all.

This French ghost town from World War II has been left as a memorial to German atrocities during World War II.

This whimsical castle of grottoes was the labor of love of a French postman, and one of the greatest achievements of outsider architecture.

19th century pendulum and a clock restored by a rogue group of guerilla artists.

Egyptian Revival movie palace abandoned for decades and restored in 2013.

France's national museum of scientific and industrial instruments.