One of Antoni Gaudí’s earliest buildings, built between 1886 and 1890 for the industrialist Eusebi Güell.

An open-air "garden" of mural art that changes weekly.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

A cemetery in Barcelona's Poblenou district is home to this touching funerary statue, which depicts death in the form of a winged skeleton.

Occupied for six centuries by Franciscan Order nuns, this monastery is an amazing ode to Catalán Gothic architecture.

This Funeral Hearse Museum represents the finest in cadaver transportation.

This historic island prison holds one of the dungeons from the Count of Monte Cristo even though it is a work of fiction.

Walk through living pictures and music in the Cathedral of Images.

A unique underground structure dating back to the 1st century BC.

This ancient theater was once the home of fierce gladiatorial battles.

A once-thriving hotel in the Swiss Alps couldn't compete with climate change.

A museum dedicated to the strange and extravagant costumes and memorabilia of the mummers, a tradition older than Philadelphia itself.

Dr Barnes' $25 billion private collection of art and arboretum.

America's most famous museum of medical oddities is home to the remains of Albert Einstein's brain.

Bar full of oddities, specimens, artifacts and homages to the great dime museums of the past.

A three-story tower of books about Abraham Lincoln is one of the more unusual monuments to the president.

The institution is sitting on a goldmine of 21,000 paints, varnishes, pigments, and primers preserved for posterity.

A fantastic array of trays and cables once whisked books over to the Capitol at 600 feet per minute.

The hidden offices underneath Memorial Bridge have been locked up since 1976.

In the basement of the U.S. Capitol Building is a hidden storage room full of ornate floor tiles leftover from the 1850s.

A celebrity from the late Cretaceous period.

A super-sized promotional trick that is now a D.C. landmark.

The most decorated dog of World War I is preserved in the Smithsonian.

The winding route passes through an enclosed alleyway, two tunnels, and leads to the White House basement.