The abandoned zoo enclosures offer a perfect place to experience the other side of the bars.

2300-year-old Roman road connecting the empire.

One of Catholicism's four major basilicas has a series of papal portraits that are said to predict the end of the world.

Ancient ruins hidden underneath a modern luxury hotel.

Brass cobblestones mark the places where individual Holocaust victims were taken from their homes.

The spot where the fascist dictator made some of his most famous speeches including declaring war on Britain and France.

Roman-era ships unearthed...

More sculpture than building, this architecturally significant temple was built on the spot of Saint Peter's crucifixion.

The privately owned cemetery that holds room for Washington's finest when they step down from life.

The "lovely red Vega" of the legendary record-settling pilot.

There's a crumbling old mansion inside the Smithsonian National Zoo.

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

During the Industrial Revolution this “Temple of Invention” was full of intricate miniature machines and gadgets.

Home to items never before seen by the public.

London's amazing modernist public square that never was.

Tucked away in the Tower of London is the weapon once used to execute high-profile prisoners.

The library houses an incredible collection of some of the world's most impressive books and manuscripts.

This marine reptile was discovered by one of the 19th century's greatest fossil hunters.

The "lost friend” is the most famous of the six moai statues that were removed from Easter Island.

An eccentric 18th century naval officer built a ship's quarterdeck on his roof, the inspiration for Mary Poppins's "Admiral Boom."

19th-century scientists would make the pilgrimage here to verify the precision of their measuring sticks.

Public access to clean drinking water was an instant hit among the masses.

Eclectic final resting place of the controversial explorer.

A statue marks the exact spot where The Boy Who Never Grows Up made his first literary appearance.