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

The water-powered carriages are long gone, but for over a century this funicular railway has been the fastest route to the highest point in Paris.

One of the greatest maze designer’s greatest mazes.

A grotto-like lodge decorated with gilded mosaics, rocks and a noisy waterfall was the setting for the most sumptuous pleasure house of 1900s Europe.

Known as the "Dodo Manège," this carousel features a herd of animals that have disappeared—or may be gone soon.

Medieval museum built over Roman baths that features famous tapestries of a lady and a unicorn.

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

This massive library holds what was once the largest book collection in the world.

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

Abandoned railway line circling the city of Paris.

France's most famous cemetery, with some of its most curious tombs.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

This Scottish burial tomb once held hundreds of ancient eagle bones.

Thanks to both terrific preservation and historic vandalism this ancient site is known as the "Heart of Neolithic Orkney."

The true age of this ancient stone circle is unknown, but its stunning vista isn't in question.

An oddly conical beacon perched atop beautiful Irish cliffs.

The skeleton of a whale that beached itself in this Irish town is now on display in their public park.

A gated cross stands on the site where an Irish revolutionary met his end.

One of the most popular megalithic sites in Ireland stands as a humbler version of Stonehenge.

This floating garden in the sky is straight out of a fairy tale, but the real thing is nothing short of magical.