This Roman amphitheater is said to be King Arthur's legendary Round Table.

This Welsh village gave itself a ridiculous name in a publicity stunt a century ahead of its time.

The Stonehenge of Wales is one of the grandest neolithic dolmens still in existence.

Hundreds of prehistoric stones, arranged in perfect lines in a French field.

The largest and most well-preserved petroglyph site in the Verde Valley.

Eons ago, a rushing lava river formed this pristine passage through solid rock.

Ancient pueblos built into the base of a natural canyon wall.

A planet-hunting astrograph built in the 1920s to seek out the so-called "Planet X" beyond Uranus.

This Arizona observatory is famous for investigations into Martian life, and as the place humans first spotted Pluto.

The final resting place of the businessman-turned-astronomer who helped discover Pluto stands near his observatory.

A mass grave for victims of an airline disaster that led to much-needed safety improvements for commercial flights.

A nature and cultural preserve named for its multitude of petroglyphs carved by the Northern Sinagua people.

This 1930s log cabin began as a taxidermy museum but is now a popular country music venue.