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

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

Legend says this rock was once a chopping block for public executions.

The steel cable lets adventurers zoom between two mountain towns at speeds of up to 75 miles per hour.

In a quiet north Chicago neighborhood rests a stunning relic of the golden age of earthenware design.

These magnificent city walls rise from the barren sun-baked Spanish plains like something straight out of a fairytale.

An otherworldly alpine pasture with its own unique microculture that recalls Middle Earth.

After years of slow decline, a derelict Gothic castle is now being restored to life.

This giant urban staircase was built to keep the city's brave fighting men from getting waylaid in the red light district.

The "stairway to heaven" lookout tower was built to resist weather, arson, and the laws of physics.

One of the deepest indoor swimming pools in the world.

The city of Palestrina was built around this magnificent terraced sanctuary dedicated to the pagan goddess Fortuna.

This cafe offers a curated collection of treats and tipples made by monks and nuns.

This mosaic-lined medieval church was built by the world's first admiral and still holds mass in ancient Greek.

One of the largest artillery pieces in the world sits in a Washington D.C. parking lot.

The enormous 250-room Vanderbilt mansion conceals hidden doors and secret passageways.

The bronzed skull of a beheaded traitor was affixed to the city gate in the 17th century.

A cablecar-station-turned-revolving restaurant with 360-degree views of the Swiss skyline.

In terms of history and architecture, this is one of the most remarkable cemeteries in the world.

An ancient octagonal weather station named for the eight Greek gods of wind.

The world’s largest collection of Tiffany glass sits in a warehouse in Queens.

England’s ancient oak tree has such an impressive girth, people have been hosting parties within the hollow trunk for centuries.

An early work of the architect Álvaro Siza Vieira, these swimming pools blend into the beach.