The last remnants of a massive medieval wall that once encompassed the city of Berlin.

A socialist building dedicated to teachers showcases one of the largest Soviet mosaics in the world.

A monument to the man who almost killed Hitler.

A statue of Vladimir Illyich Lenin guards this abandoned building in the "Forbidden City."

Several of these strange cone-shaped bunkers can still be seen around the former Nazi headquarters.

The ruined remains of the airport Claus von Stauffenberg departed in his failed attempt to kill Adolf Hitler.

For patriotic Russians, this memorial honoring the Soviet soldiers who died liberating Berlin in 1945 is the most sacred location outside of Russia.

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

This World War II bunker now survives as a documentation of the Nazi regime and war crimes.

Berlin's oldest surviving academic architecture hosted decades of animal dissections.

The world's first clock to use set theory as a measure of time required the invention of a new light bulb just to maintain its obtuse measurements.

This stone amphitheater was once part of Nazi Germany's plan to promote propaganda.

An abandoned swimming pool decays on the outskirts of Berlin.

The final resting place of many of Germany's most famous communists.

Twisted trees shaped by coastal winds make this woodland look like something from a spooky story.

A museum dedicated to the history of a terrifying secret police is now held in their former headquarters.

A century-old shot ball factory tower is open to the public once a year.

"There's nothing there," and other lies the KGB told us.

An underground nightclub helped spark a "Singing Revolution."

This former medieval prison now unlocks Estonia’s rich photographic history.

An abandoned textile factory on the "island of crows" was home to Estonia's first workers' strike.

Visitors can sit and study the board with this Estonian chess legend and International Grandmaster.

Only a fragment of this 15th-century Dance of Death survives today.

The oldest church in the Estonian capital is home to over 100 fantastical cemetery coats-of-arms.