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

The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

A 200-year-old bar in the historic French Quarter refuses to give up its place in history, nor its role in securing ours.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

Hear the quietest sound from across the dome.

The world's longest known cave system.

The Denver airport is guarded by a 32-foot-tall sculpture of a demonic horse.

Breathtaking and huge 430 year old maps of Italy.

Giant, natural amphitheaters made of delicate geological formations called "hoodoos."

Strange red rock formations that have been attributed to a higher power for hundreds of years.

A beautiful geyser under environmental threat.

This 4,000-foot-diameter hole is touted as "the most well known, best preserved meteorite crater on Earth."

A monument celebrating the idea of reaching inaccessible places.

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

The fairy tale castle of the "fairy-tale king."

World's first "penitentiary," meant to be humane, drove men insane.

Elevated freight railway turned wildly successful urban park.

Famously misunderstood wonder of the ancient world

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

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

Macabre astrological automaton clock dating to the late 1400s.

The haunting "Hell House Altar" is one of the few remnants of an abandoned college that has been a magnet for local legends.

The semi-reclaimed ruins of this canal were once part of an ambitious plan to reroute the mighty potomac.

The United States Capitol's former columns still stand.