Also known as "Robin Hood's tree," this tree became a famed location along Hadrian's Wall before it was cut down in an act of vandalism.

A massive underwater sinkhole made famous by Jacques Cousteau.

A volcanic tunnel illuminated by natural skylights offers a shaded respite from the desert sun.

A former utopian healing center created by a huckster and built by derelicts.

No one's quite sure why there's a metal megaphone bolted on two rocks in the middle of the Mojave Desert.

One of the great treasures of Neolithic art lies within this carefully constructed pile of rocks.

Over 20,000 sets of spice shakers reveal the surprisingly telling history of our most basic spices.

A tunnel with windows, so you don't miss out on the impressive views.

One of the most spectacular bridges in Spain spans a narrow chasm that divides the city of Ronda.

These ancient giraffes are the largest known animal petroglyphs in the world.

A stranded woman lived alone on this remote island for 18 years, inspiring the great children's novel "Island of the Blue Dolphins."

A natural formation that resembles a camel resting in the New Mexico desert.

A spoke-tacular artwork constructed from recycled bicycle rims.

Legends surround this jagged rock formation in the New Mexico desert.

Fourteen curious and controversial white bunnies sit in a circle near Newport Beach City Hall.

Museum dedicated to the preservation of surf culture.

L. Frank Baum wrote part of the "Wizard of Oz" series in this wooden Victorian beach resort.

These hellish-looking cliffs in the Canadian Arctic have been burning for centuries.

A boiling wellspring flowing with natural gas burns in a continual blaze.

A toxic ghost town sitting atop a massive coal fire.

A natural gas leak provides a flickering flame beneath a waterfall.

A coal fire has been burning underground here since 1896.

Flames have been burning within this mountain for more than 2,500 years.

A shrine of fire worship built on top of a natural flame.