A vista of the city and sea from atop the little-known viewing deck on an unassuming Columbus statue.

One of the most photographed buildings in a city known for its Modernista architecture is an abandoned squat.

Barcelona's historic 19th-century sewers, whose foundations were laid in medieval times, are open to the public for exploring.

Turntable anonymously received orphans, alms, and groceries.

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

This small museum collects the Christian remembrances which would otherwise be forgotten.

A former plague hospital turned medical museum.

This 1920s Amsterdam neighborhood was built as a giant experiment in concrete construction.

This gorgeous reading room houses the oldest and largest art history library in the Netherlands.

The world's first zoo for microbes collecting the horrible and wonderful things living on and around us.

The world's oldest Jewish library was founded by Sephardic Jews in 17th century Amsterdam.

Step back in time and witness the fall of Constantinople.

The eclectic home of a leading Turkish architect is a gorgeous piece of eye candy.

The ornate miniature mansions were built for Istanbul's feathered residents.

The most metal church of all time was built in record time because of an international, pious pissing contest.

This museum was invented in a novel before being made real by the author.

Cozy basement bar sports an inventory of over 2,000 beers.

Experience architect Le Corbusier's modernist design for living in the home he designed for himself.

High atop the Eiffel Tower is a small apartment built exclusively to entertain the science elite and make the rest of Paris jealous.

The headless bodies of more than 1,300 guillotined victims of the Reign of Terror are buried here in mass graves.

The oldest and smallest cemetery in Paris is only open to the public twice a year.

Stripes of human ashes cover a back lawn in the most sought-after burial grounds in Paris.

This museum in a Paris apartment gives a unique look at the iconic French singer's life.

This charming cobbled backstreet is the most Instagramable street in Paris, much to the residents' annoyance.