Most-visited and most-photographed slot canyon in the American Southwest.

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

This Yellowstone geyser may not shoot as high as the nearby Old Faithful, but it erupts for considerably longer.

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

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

A beautiful geyser under environmental threat.

The fifth-longest natural arch in the world, and the longest outside China.

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

The hike through a narrow river flanked by the 2,000-foot-tall walls of Zion Canyon is one of the best in the world.

This tri-part waterfall is a little bit of fairytale beauty in the heart of Luxembourg's Little Switzerland.

Roman ruins top white travertine terraces formed by ancient hot springs.

Pilgrimage site for star-crossed lovers.

According to tradition this is the oldest church in Venice, but its actual age is a mystery.

In the past, Renaissance sex workers were encouraged to entice customers on this bridge.

This deconsecrated church has seen many uses, from a tobacco storehouse to a cinema.

The world's most charming instant portrait studio also happens to be its smallest.

This functioning parish church is also the site of many concert performances due to its wonderful acoustics.

The world's northernmost aquarium looks like it has fallen over.

The convergence of two currents makes this a surprisingly pleasant getaway in the Arctic Circle.

Cold war icon and onetime "hole" in the iron curtain.

The bunker where Hitler took his own life is hidden under this deliberately ordinary parking lot.

Thousands of coffin-like pillars make up this controversial Holocaust memorial.

The largest free-standing aquarium in the world resides in a hotel lobby in Berlin.

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