This public observatory is home to the "celestial cannon," the longest pointable telescope in the world.

Enter the cabin of a life-sized Hindenburg replica.

A former ironworks that was the first UNESCO industrial site.

The skeletal frame of a decommissioned gas-pumping station offers breathtaking views of greater Berlin.

Super-heavy Nazi architectural experiment.

An elevator into the Baltic Sea.

This Berlin island is home to a flock of free-roaming peacocks, as well as a historic ivory folly.

Where beer lovers can literally immerse themselves in beer.

Giant WWII fortresses that fired 8,000 rounds a minute, now home to thousands of pigeons.

A Soviet era flat that refused to conform to the dull gray standards.

The shattered remains of the world's once tallest structure.

The largest toy museum in Poland showcases Europe's history of childhood.

This picturesque castle in Poland has a rich history, including a legend that ties it to lost Incan treasures.

Poland's oldest salt mine has nearly everything one needs to live underground forever.

At first glance, this area seems like just another city park, but the lush landscape hides a dark past.

The site of the first battle of World War II.

An underground city of salt.

This museum in the tower of the oldest church in Gdańsk, is home to centuries-old time-keeping devices and the world's first pulsar clock.

This man-made mound monument was built out of soil from all across the Polish empire.

This 700-year-old structure is one of the most unique architectural and historic monuments in Gdańsk.

The oldest wind turbine in Europe, constructed by a group of friends in 1932.

A World War II torpedo launch station abandoned off the Polish coast.

This open-air museum was originally a World War II testing ground for German missiles and rockets.

This decommissioned nuclear power plant offers tours of its Communist-era control room and reactor hall.