A petroglyph map of the upper Snake River carved by prehistoric hunter-gatherers.

A violent name for a violent volcano.

This rare volcano spews the strangest and (literally) coolest lava in the world.

The world's first and only natural nuclear reactor.

Hidden behind Lincoln's head is a 70-foot-long chamber containing enamel plates documenting American history, sealed in a teakwood box in a titanium vault.

A modern mechanical planetary system, part of a 10,000 year clock.

Two hundred tons of pioneer artifacts were painstakingly recovered from a shipwreck at the bottom of the Missouri River.

A whimsical, punny collection of "fence art" outside the tiny mountain town of Baker, Nevada.

An ancient instrument used to measure the waters of the Nile so Egyptian farmers would know whether to expect famine or flood.

This bug-eyed water wheel uses the power of the Sun to clean up Baltimore Harbor.

An unrecognized nation-state created in the 1820s to avoid taxes.

The first presidential bomb shelter was located in an old vault under the Treasury, connected to the White House via tunnel.

A hermit's tiny cell built into the cliffside that saved him in South Pembrokeshire.

A perilous medieval road leading right into the sea.

What might look like a cliffside sacrificial altar at first glance is actually a stone compass pointing to cities and lighthouses all around the world.

The giant Siberian crater known locally as the "doorway to the underworld" is expanding every year.

This mysterious underground cave in Shropshire dates back to the 18th or 19th century.

The ancient mosaics here are considered among the finest in the world, and serve as a stunning record of Greco-Roman daily life.

This dramatic landscape hidden on the Isle of Skye looks as though you've stepped into the magical realm.

A historic London pub with prison cells in the cellar and a "spy room" on the second floor.

The Grand Canyon of Texas.

The most iconic structure in Scotland has been home to bishops, colonels, and Sean Connery characters.

These fantastically named natural pools look like something out of a Scottish myth.

A small island abbey is the final resting place of many medieval Scottish monarchs, including the real Macbeth.