A semi-scholarly approach to sex.

This historic address is home to the beloved ball and is an almost totally empty building among the most expensive real estate in the world.

A forgotten relic from New York's bygone trolley system hides in plain sight under a bridge.

This daunting 1st century fortress was purportedly the site of one of the most dramatic revolts of the Jewish-Roman wars.

The tallest waterfall in the Judean Desert is named for its connection to a biblical figure.

This incredible stone temple is a monument to death, victory, and fantasy architecture.

This full-sized orange tree lives suspended in mid-air above the streets of Jaffa.

This site honors an Israeli cargo ship that was destroyed by the government in 1948.

Once the tallest building in the world, this abandoned church is now a monument to the destruction of WWII.

Hamburgers are intensely proud of their tunnel beneath the river.

Model Trains and Much More in Hamburg.

A plaque marks the spot where the saint was shoved off the Charles Bridge and into the river.

An architectural oddity hides in plain sight on this iconic London bridge.

A fantastic castle rumored to be the birthplace of King Arthur.

Sometimes an island, sometimes a rocky outcropping connected to the world by a tiny suspension bridge.

This ancient stone bridge dates back to the early Middle Ages.

One of the few standing Roman lighthouses and a labyrinth of tunnels are a couple of the secrets at this historic castle.

Time stands still at this serene burial ground in the center of Budapest.

The largest statue of this convex, homogeneous object with just one stable and one unstable equilibrium point.

The Grand Mall in Varna hosts one of the biggest collections of Soviet-era paraphernalia in Bulgaria.

This once-grandiose behemoth of a monument from the socialist era now sits quiet and closed up.

Massive, unfinished broadcasting station stands as a monument to the fall of communism.

The site of many battles and tragedies, including the 40 maidens who leapt into the sea.

Twisted buildings adorn the banks of the Rhine river.