A German apartment building hosting as many trees as human occupants.

One of the largest caves in the world open to the public.

One of the best-preserved Roman amphitheaters is still used today, but for less brutal events.

This truly palatial work of Communist-era architecture now sits crumbling on a Croatian beach.

The only gulag ever to exist in socialist Yugoslavia.

The remains of a sunken military ship wreck visible through clear water.

This military tunnel dates back to World War II and provides visitors with a little wartime adrenaline.

Now abandoned, the world's first torpedo factory is crumbling into the sea.

Croatia's "hairy stone" fortress is one of the most well preserved Istrian castles.

This massive subterranean fissure is known as the "underground Grand Canyon."

Castle and secret tunnel withstood a siege until its owner was killed by the Holy Roman Empire, while sitting on the toilet.

The "dragon babies" of southeastern Europe.

A miniature train-ride through Slovenia's largest cave system.

The largest treasure hoard in Europe is contained in a castle that was bombed out during World War II.

It has an American Dream Car exhibit, Europe's largest Formula One collection, and many, many mannequins.

Along the banks of the River Rhine lies a park that seems unassuming, but beneath the surface lies a long and fascinating history.

While you wait to cross the street at a traffic light in Mainz, you might notice that the light is staring back at you.

Germany's longest suspension rope bridge.

A magnificent place to see authentic paleolithic cave paintings that are an astounding 33,000 years old.

A road that winds through this natural cave is the only way to access the small, appropriately-named village of Cuevas.

Single runway interrupted by a busy road that cuts across its middle.

On La Gomera, "Silbadors" communicate in a 4,000-word language of whistles.

Partially collapsed lava tube and cave system complete with concert hall, underground pond, and unique albino crabs.

The chefs at El Diablo use heat generated by an active volcano to cook the food.