Head underground and take a tour of the city's working sewer system, and see the underground river Senne, which defined Brussels for centuries before being covered in the 19th century.

Nature is slowly overtaking this disused cemetery on the outskirts of Brussels.

This tremendous timepiece was once the largest cuckoo clock in the world.

The final resting place of the famed German pilot, the "Red Baron."

This ornate Weser Renaissance house was also the home of an infamous witch hunter.

The sweet story of how American cargo planes became known as "Candy Bombers" during the Berlin Blockade.

Carved fountains poignantly placed in parks and in front of special monuments.

Some people believe that this makeshift space monitoring station received transmissions from clandestine cosmonauts.

The astonishing collection of an infamous criminologist.

The intricate geometry inside this Baroque-style dome was designed to create "terror of the human soul."

A landmark in the history of technology and computing is hidden in a tiny Baroque chapel.

When a conglomerate of visionary startups commandeer a disused Greek Orthodox Church, zaniness ensues.

These airport hangars are now a bustling shopping center with only hints of its past still lingering.

Metro station with a claim to rock n' roll fame.

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

An 18th-century post box used to alert the church of sick and ailing foreign pilgrims.

A massive marble foot is tucked away in a small alley near the Pantheon.

This medieval church in Rome was almost destroyed following a terrorist attack in 1993.

This small church was constructed over the ruins of three temples dating to the Roman Republic.

This is the oldest Roman-made bridge in the city still existing in its original state.

The only remaining arch of the oldest stone bridge in Rome stands in the middle of the Tiber.

This gallery commissioned by Cardinal Spada is known for its magnificent optical illusion.

This hidden alley near the location of Rome's first theater was the site of a curious miracle.

Romans decided this 16th-century "talking statue" was so ugly, they named it after a primate.