The largest Art Nouveau complex in the world is a Barcelona hospital with a 600-year-long history.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

A cathedral resurrected from the ashes of one of Europe's greatest urban fires.

Finland's oldest astronomical observatory once played a crucial role in seafaring and timekeeping.

In the Hugging Tree Forest, lingonberry marshmallows, hot chocolates, and the best campfire lattes north of the Arctic Circle come to you.

Once a 19th-century brasserie, this McDonald's exterior celebrates Alsatian design and the "King of Beer."

The tomb of history's greatest potato promoter is surrounded by tubers.

The storefront of a ramshackle Parisian puppet theater.

This recessed garden protects thousands of mountain plants by creating its own microclimates.

Collection of antique taxidermy and natural specimens, near one of Paris's oldest flea markets.

The personal library of the founder of modern neurology is open to visitors.

The narrowest street in Paris.

The spiral staircase hidden inside this giant Parisian column was likely built for Catherine de Medici's astrologer.

Pitié-Salpêtrière was the dumping grounds for women who received the dreaded diagnosis of "hysterical."

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

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.

The first green space constructed on an elevated viaduct.

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

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

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

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

Indents in the pavement are all that remain from a grisly death machine in Paris.

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

Walk upon the mementos of the dead in this Parisian courtyard paved with medieval tombstones.