Stockholm's deepest subway station is also a stunning ecological wonder.

An Italian hillside ghost town.

Natural cathedral designed by Italian artist Giuliano Mauri.

Abandoned medieval hill town.

2300-year-old Roman road connecting the empire.

Ruins of a 10th century church tucked away deep in a botanical garden.

A large grotto built in the 16th century amidst Florence's famous Boboli gardens.

The only "Egyptian" pyramid in Europe and the legendary tomb of Remus.

This 16th-century monastery has been turned into a surrealist architecture compound.

As can be expected from a centuries old church built in a canal city, the undercroft of this house of worship is beautifully flooded.

The yawning maw of this pagan visage is said to bite off the hands of liars.

The underground sanctuary of a mysterious ancient cult.

The glowing blue Nymphaeum of Emperor Tiberius.

Venice's "Island of the Mad."

According to the local folklore, the myriad colors of this lake are the result of a lovelorn wizard's blunder.

Geothermal waterfalls in Tuscany.

Architectureal fantasy quarter of Rome.

Stalactites and stalagmites in a beautifully lit cave.

Renaissance villa and gardens complete with a tormented colossus.

Pompeii's less famous neighbor is still revealing her secrets.

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.

Vienna's underworld of tunnels and subterranean rivers made an iconic appearance in a 1949 Orson Welles film.

Collection dedicated to funeral rites, equipment, and mourning rituals of the Viennese.