This abandoned, windowless concrete block is one of the strangest buildings in Tulsa.

Trick water gardens from 1619 featuring a 200 piece mechanical theater powered by water.

The highest cold-water geyser in the world.

The lighthouse is on a island which is connected to another island, which is connected to another island, which is connected to one of the largest islands in the world.

Horrifically creative torture devices and shame punishments line the walls of this chilling museum.

In this brilliant blue spring in Germany, legend has it that a sad mermaid learned to finally laugh.

A tour of underground Berlin takes you through WWII air raid shelters and tunnels used to smuggle people out of East Germany.

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

The former private quarters and office of Dr. Sigmund Freud now hosts a museum housing the works of the founding father of psychoanalysis.

One of the best collections of wax anatomical models in the world.

The skulls and bones of thousands of soldiers line the walls of this small Italian chapel.

The bones of some 7,000 soldiers killed in the historic Battle of Solferino are stored here.

The skull of this patron saint is kept in a shrine located in his hometown.

A museum and apothecary garden devoted to the history of frontier medicine.

The Tübingen University anatomical collection hosts an example of an extremely rare medical phenomenon.

This ossuary is more than five centuries old and is heralded as one of the finest in Switzerland.

Once a farm where patients tilled the soil, this asylum lost its workforce when overmedicating became common practice.

Nicknamed the 'Chestergate Hotel,' the underground tunnel had beds, lights, and even flushing toilets.

Rustic natural hot springs in the deciduous rain forest.

This giant tower beacon was a key navigation tool for pilots delivering mail amid the night skies.

A former sanitarium where soldiers were sent to recover in the healing waters of hot springs.

One of the "twins" in these falls on the Snake River was sacrificed for hydropower generation in the 1930s.

An impressive waterfall nestled in the cliffs of Idaho's Snake River Canyon.

This underground cave located in the most barren reaches of Idaho is filled with ice year-round.