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.

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

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

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

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 iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.

Celebrated in poem, this tiny hidden cemetery has a big and grisly history.

A Victorian marvel of engineering is now a 21st-century tourist attraction.

The "Black Arch" guards the entrance to the picturesque Glens of Antrim.

The ruins of this medieval castle in Northern Ireland have inspired artists from C.S. Lewis to Led Zeppelin.

This 18th-century fort surrounded by a moat was used to store gun powder and ammunition, and now sits in the middle of a large part in Dublin.

This former World War II torpedo testing location is now an important nesting site for migratory birds.

This mysterious Bronze Age standing stone has become a place where couples profess their love.

This village provides a glimpse at rural life in Northern Ireland during the mid-20th-century.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

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

Once the longest bridge in Ireland, this rusting span sits abandoned and overrun by nature.

The oldest inn in Kilkenny was established by the first convicted witch in Ireland.

This Irish show cave is said to have been the site of a Viking massacre that claimed 1,000 lives.

A massive Celtic cross secretly growing in an Irish forest.