Tables of secondhand books fill the inner courtyard of this 17th-century stock exchange.

This triumphal arch celebrating the Sun King's conquest of Lille is a masterpiece of military architecture.

A mysterious chasm in the heart of the ancient Roman Forum, the Lacus Curtius was once believed to be a gateway to hell.

Plaques on its facade commemorate the Tiber's most destructive deluges.

A detailed pachyderm supports Rome's smallest Egyptian obelisk.

2300-year-old Roman road connecting the empire.

This private skyway is filled with art and was expanded explicitly so that Hitler could appreciate a river.

This Renaissance palace features a unique architectural design and is now home to the Ferrara National Art Gallery.

Thousand-year-old Viking runes adorn an ancient Greek lion at the entrance to the Venetian Arsenal.

Two stone columns flank the grand Venice square, but there were supposed to be three.

Go inside to really appreciate this 500-year-old technological masterpiece.

The pile of books behind the dignified writer gave the statue a most undignified nickname.

The secret medieval communication system will whisk your words above the noise of the crowd.

Milan's duomo is covered in beautiful carving including a curious "dinosaur-like" beast.

The castle where Martin Luther secretly translated the New Testament from Greek to German while in hiding.

The largest free-standing aquarium in the world resides in a hotel lobby in Berlin.

Reminders of the Battle of Berlin still scar the railway.

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

The most visited, and possibly most controversial, museum in Germany.

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

A fascinating insight into daily life in the Eastern Bloc.

Tiny memorials honor individual victims of the Holocaust.

Thousands of coffin-like pillars make up this controversial Holocaust memorial.

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