A letterbox installed specifically for the first editor of the Oxford English Dictionary.

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

An abandoned NSA listening post on Berlin's "Devil's Mountain."

The world's first clock to use set theory as a measure of time required the invention of a new light bulb just to maintain its obtuse measurements.

Known simply as "The Hand," this famous public sculpture in Berlin was featured in a Depeche Mode music video.

A wunderkammer of mysterious objects and stories.

The last remnants of a massive medieval wall that once encompassed the city of Berlin.

A unique Holocaust memorial tells the personal stories of the Jewish residents exiled from greater Berlin.

This platform is now a memorial dedicated to those who were deported during the Holocaust.

A surreal museum of extraordinary industrial objects.

A bronze of the man in all his sinewy glory celebrates his longtime connection to the Ohio city.

Known locally as "the giant head," this 14-foot LED sculpture has a photo booth in the neck where you can have a 3D picture taken and displayed.

An historic and oft-filmed spot for musclebound iron pumpers on the Pacific coast.

Central America's deepest lake is actually a volcanic caldera, surrounded by three volcanoes.

Faceless white figures loom over the city from the rooftop.

San Francisco's oldest surviving monument and meeting place for 1906 survivors.

A six-ton wedding present for the King of the Scots.

The most loyal of little dogs, or a Victorian era publicity stunt?

The final resting place of soldiers' loyal canine companions.

Protecting the dead from opportunistic body snatchers.

360° views of the city plus five floors of optical illusions and hands-on science.

This 17th-century street hidden beneath Edinburgh was once a breeding ground for the black death.

Displaced highlanders would take shelter from the wet Scottish climate under the large walled bridge at Glasgow Central Station.

This stately monument has been wearing a traffic cone hat for decades much to the delight of the locals.