A lush green oasis in the middle of Chicago.

Four glass boxes hover over 1,000 feet in the air to give visitors an unparalleled view of Chicago.

Legend has it the commander of the defenders drew a fateful line in the dirt with his sword just before the final battle.

This erect, phallic geological spire wasn't always named so domestically.

In its day this historic fort held 100 cannons pointed in almost every direction to protect New York.

A centuries-old lookout post still sits atop a natural stone spire.

Modest by day, illuminated majestically at sunset.

Hidden in the shadow of a rocky fortress is one concubine’s long-forgotten legacy.

A blooming house of worship for the masses.

This hilltop warren of monastic dwellings is the result of centuries worth of Mongol attacks.

This otherworldly palace-mausoleum complex is the stuff eternal dreams are made of.

Once an indicator of social class, the color blue has come to define this city on the edge of the Thar Desert.

A former steam-powered mill from the 1800s is now an industrial park with a giant steel dragon slide.

This former Baroque palace on the historic Calle Montcada is a rare architectural gem and was once the meeting place of an aristocratic scholarly society.

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

This semi-secret storybook hedge maze is also the oldest garden in the city.

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

A marvel of technology a century ago, this disused power station now offers a lovely glimpse into the industrial design of the past.

A two-way chairlift system between Zugliget and the highest point in the city.

Built in 1870 at the bridge that connected Buda and Pest, this spectacular incline railway was almost lost forever during World War II.

This Hungarian castle was built out of cardboard and wood until it proved so popular that it got upgraded to stone.

Vienna's giant wonder wheel had a starring role in one of the greatest noir movies of all time.

This cubist Vienna church building looks like some sort of alien stonehenge.

Located right outside of Vienna, visitors can take in expansive views of an ethereal forest.