The last physical evidence of the Lewis and Clark trail is one of their autographs etched into this giant rock.

Derelict buildings are all that remain of a complex at the site of one of the worst mining disasters in Montana history.

The largest earthwork effigy in the world.

A mysterious monument meant to be a guide into "an Age of Reason" was destroyed after an apparent bombing.

For hundreds of years, automatons moving to metallic music have been marking the passage of time.

Arthur, Merlin, and Guinevere are among the largest and oldest satellite dishes on the planet.

The spiral staircase hidden inside this giant Parisian column was likely built for Catherine de Medici's astrologer.

"Dark Sky Park" is heaven on Earth for astronomers, one of the rare U.S. locations with no artificial light pollution.

This humble star-gazing center touts itself as the "Birthplace of American Astronomy."

Home of the International Space Hall of Fame.

The world's first commercial spaceport is a disappointment of cosmic proportions.

The artist James Turrell is repurposing an extinct volcano crater as an observatory to experience the cosmos.

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

These four islands right offshore have waterfalls, colorful lights, fancy buildings, and a secret purpose.

The final resting place of a space program monolith.

Macabre astrological automaton clock dating to the late 1400s.

The world's oldest Jewish library was founded by Sephardic Jews in 17th century Amsterdam.

A fantastic array of trays and cables once whisked books over to the Capitol at 600 feet per minute.

The mysterious headstone of an unidentified bank robber was seen visited, every year, by a woman in black.

A succinct inscription commemorates the ebb and flow of a woman's life.

His body was found mysteriously preserved in a Swedish mine over 40 years after his initial disappearance.

The remote graves mark the mysterious deaths of four 19th century explorers.

One of the only spherical 19th century gas containers left today.

A daily replay of the experiment that proved the rotation of the Earth.