One of Madrid's oldest trees, with a long and colorful history, resides in El Retiro Park.

This lucky bronze frog was gifted to Madrid by a casino.

A lush indoor jungle fills this bustling Madrid transportation hub.

For decades, Puerta del Sol has been illuminated by a giant, guitar-wielding bottle of sherry.

This sweet-toothed bear searching for snacks has been a symbol of Madrid for decades.

A stone slab in Madrid marks the point from which the distances of Spain's national roads are measured.

An open-air, roadside eatery celebrating a historic indigenous cuisine of complicated significance.

Where once there was a train station bathroom, there is now this German burger joint.

Reminders of the Battle of Berlin still scar the railway.

A memorial in the Tiergarten is a reminder of the suffering inflicted on homosexuals by the Nazi regime.

A monument to the man who almost killed Hitler.

The bunker where Hitler took his own life is hidden under this deliberately ordinary parking lot.

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

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

This obscene artwork on the side of a newspaper office pokes fun at a rival paper's former editor-in-chief.

Dedicated to the European Sinti and Roma peoples murdered during the Holocaust.

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

Tiny memorials honor individual victims of the Holocaust.

Cold war icon and onetime "hole" in the iron curtain.

Dedicated to nine marines from Massachusetts who perished during the Beirut bombings.

The site of the famous Nazi book burning campaign of 1933 remembers its "Night of Shame".

An ornate private entrance to the Vienna subway built specifically for the emperor.

Built to give thanks for the passing of a plague epidemic, this cathedral is a one-of-a-kind architectural hybrid.

On a winding Vienna side street, one museum has turned their windows into a monument to history’s peace-minded heroes.