This memorial commemorating fallen Swiss Guards of the French Revolution has been called the saddest stone in the world.

A crumbling World War I fort that is reached through a series of concrete tunnels.

An organ located deep within a cave, whose "pipes" are the geological features of the cave itself.

This mosaic dedicated to John Lennon was tended for years by a Beatles super-fan.

One of nature's most well-scheduled phenomenons resides in Wyoming's Yellowstone National Park.

Frank Lloyd Wright's most iconic home dangles over a Pennsylvania waterfall.

One of the most scenic stretches of road in America winds between some of the country's oldest trees.

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.

The first declared National Monument in the United States.

The deepest lake in the United States, and once the site of epic destruction that lives on in legends.

The last moments of the ill-fated Pompeiians, frozen forever in plaster.

The ruins of a medieval monastery named after a type of tree.

A formerly glacier-tipped volcano that inspired none other than Jules Verne.

This valley of hot springs and boiling mud pots is home to the record-holding "Geysir," which originated the English word.

This elegant arc of a waterfall marks a religious turning point.

The most powerful waterfall in all of Europe.

An encyclopedic collection of mammal penises.

Iceland's largest lagoon is home to stunning multi-colored icebergs.

One of the tallest buildings in Iceland, and perhaps, the most visually impressive.

The unique waterfall in Iceland's south features a backdrop of geometric black lava columns.

Medicinal spa created with the discharge from a geothermal energy plant.

The only "Egyptian" pyramid in Europe and the legendary tomb of Remus.

Despite violent work crews and massive delays this abandoned canal tunnel was built to last into the modern day.

An almost life-sized elephant named Ms. Ellie greets visitors at this jumbo-themed museum.