The walls and ceiling of this Polish church are decorated with thousands of skulls, with another 21,000 skeletons just below.

Amsterdam's former hotspot for public executions and dissections.

A Portuguese Jewish cemetery filled with stunning grave monuments that date back to 1614.

The history and future of cannabis.

Museum preserving torture methods from the past.

The tunnel's elegant proportions keep you snug with no claustrophobia freak-out.

The hidden lair of an alchemist rediscovered in a 2002 flood.

The site where a plot to assassinate Hitler was planned—and its conspirators were executed—is now a powerful memorial to the German resistance during World War II.

The original burial place of this preeminent 18th-century Jewish philosopher was razed by the Nazis.

A towering monument to war, located on a beautifully peaceful hill.

Tiny memorials honor individual victims of the Holocaust.

One of downtown Berlin's last reminders of its Communist past.

These brass bunnies honor the rabbits that dominated the no-man's-land around the Berlin Wall.

These former Nazi anti-aircraft towers offer a singular view of the north of Berlin in the summer, and a sanctuary for bats in winter.

The walls of Germany's Parliament still show the scars of the Red Army takeover in World War II.

A unique Holocaust memorial tells the personal stories of the Jewish residents exiled from greater Berlin.

On the Spree bank, discover one of the last reminders of a symbolic wall that divided, and was torn down by the people.

This Polish cave has housed a dragon, a brothel, and an enduring legend.

Real bones which are said to have belonged to a Polish dragon.

The metal leaves on this tree are engraved with the names of Holocaust victims.

This building has survived for more than a century and remains virtually untouched.

A 13th-century convent where St. Margaret of Hungary spent her teenage years.

Late at night, the bust of the "Dracula" actor was snuck onto the facade of this Budapest castle.

A museum dedicated to a secret military hospital hidden beneath a castle in Budapest.