Castle and secret tunnel withstood a siege until its owner was killed by the Holy Roman Empire, while sitting on the toilet.

A miniature train-ride through Slovenia's largest cave system.

A World War II evacuation tunnel turned into a history display of Croatian state and people.

This communist behemoth is the heaviest building in the world and a legacy of a brutal regime.

The railway carts travelers to central Athens's highest peak, which offers stunning vistas of the city.

Berlin's old airport.

The bunker where Hitler took his own life is hidden under this deliberately ordinary parking lot.

An imperial church bombed to ruins during WWII now stands as a jagged memorial.

The "Prussian Versailles" that is as glorious today as when it was built.

Ride in 1960s style on the private luxury train Marshal Josip Tito used to travel around Yugoslavia.

This once-derelict building is now one of the most beautiful bookstores in the world.

Super-heavy Nazi architectural experiment.

Cold war icon and onetime "hole" in the iron curtain.

Thousands of coffin-like pillars make up this controversial Holocaust memorial.

Huge masonic hall in Philadelphia with lavishly themed rooms.

The sounds of the world's largest fully functioning pipe organ dazzle shoppers at a Philadelphia Macy's.

Current docking place of the SS United States, the fastest transatlantic ocean liner.

The last of Philadelphia's wood-paved streets is now a landmark of terrible engineering.

The first American department store, and home to the largest operating musical instrument in the world.

This elaborate towering structure was once famed for its revolutionary height.

World's first "penitentiary," meant to be humane, drove men insane.

Yo, Adrian!

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

It's rumored this unique Baltic beacon was designed by Gustave Eiffel himself.