The perfectly preserved underground rooms where Churchill plotted the war against Germany.

Real bones which are said to have belonged to a Polish dragon.

A modern-day Lascaux cave underneath Paris.

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.

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

Exquisite wall sculptures carved in secret by an early quarryman in an obscure corner of the Paris Catacombs.

The ruins of a Duke's bucolic dream, where camels once roamed alongside "Dutch" windmills and faux-Italian vineyards.

A Parisian cemetery where the elite and artistic are interred beneath an eccentric collection of tombs.

A subterranean shelter remains intact under a busy Paris railway station.

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

Behind the pink curtain, Au Bonheur du Jour, an art gallery of erotic archives.

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

"In the Dark" Restaurant in Paris offers dinner in complete darkness.

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

This museum houses an imposing skeleton army comprised of creatures great and small.

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

A scandalous Art Nouveau collaboration that set Paris all atwitter at the turn of the century.

A haunting collection of the vanished and disappearing natural world.

One of the oldest medical collections in Europe focusing on rare surgical instruments.

A museum of carnival attractions where you are invited to ride the rides.

A horde of stray cats rule in this secluded Parisian cemetery under a bridge.

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

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

Ottoman-era houses lovingly preserved.