This small museum tucked within a subway station holds pieces from Madrid's past.

A lush indoor jungle fills this bustling Madrid transportation hub.

An exquisite collection of fairytale conveyances that puts most car museums to shame.

Located in the thermoelectric factory that once powered the entire city, this Portuguese museum is shockingly fascinating.

This Industrial Age architectural and engineering gem helps visitors and residents alike traverse Lisbon, “The City of Seven Hills.”

This gaping hole in the middle of a remote mountain lake looks like a portal to another dimension.

The world's oldest bookshop still in operation.

Spanish architects used seized Muslim gravestones to rebuild parts of the fortress.

A subterranean house of worship carved right out of the bedrock.

A detailed pachyderm supports Rome's smallest Egyptian obelisk.

Thousand-year-old Viking runes adorn an ancient Greek lion at the entrance to the Venetian Arsenal.

Gods clash with machines in a power plant regenerated as a museum.

Secret refuge and museum of the Duke of Florence.

Filled with goldfish swimming in a shallow pool of sea water, this ancient crypt is more wishing well than burial site.

This palatial spiral staircase was so unusual the name "snail" was given to the noble family who built it.

Pilgrimage site for star-crossed lovers.

This ritzy Italian market is built around a statue of an unforgiven heretic who was burned for his belief in an endless universe.

Go inside to really appreciate this 500-year-old technological masterpiece.

Over 50 exquisite hand-painted Renaissance maps decorate a Medici storage room.

Five candy-colored villages on the Italian Riviera.

The last moments of the ill-fated Pompeiians, frozen forever in plaster.

The celebrated eyesore created by starry-eyed sweethearts.

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

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