The world's largest mountain carving could fit all of Mount Rushmore inside it many times over.

The granddaddy of all tourist traps, built on ice water, jackalopes, and a giant dinosaur.

The ruins of a stone tower with alleged (but unlikely) Roman origins.

This tall stone wall with no door and ill-matched windows was built centuries ago, and used as a shelter for domesticated pigeons.

The castle still holds traces of the abandoned Roman fort it was built atop.

This neolithic stone grave has been altered and restored so often its now more neo than lithic.

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.