This recipe is set in stone.

255 feet of suds, scrubbers, and blow dryers.

Scale replica of China's ancient terracotta tomb warriors and Forbidden City are the side project of an eccentric millionaire.

This former Texas landfill is flush with 300 million-year-old fossils, all fit for the taking.

Housed in a century-old building, this museum's dedicated not just to soft drinks, but to the free enterprise system.

An abandoned quicksilver mining town surrounded by the Big Bend parks.

A Prada store in the West Texas desert that is never open for business.

A medieval castle in the middle of rural Texas.

A 24-hour vending machine restocked daily with homemade full-sized pecan pies.

A 90-year-old underground water reservoir offers a more industrial kind of tranquility.

The Grand Canyon of Texas.

A modernist landscape of water and sci-fi concrete.

An emerald-green grotto just a short trip from Austin.

100 years later, they're still down there.

For 60 years, the academy had no permanent location until members voted Washington D.C. as its forever home.

The Byzantine, pre-Columbian, and medieval art at this stately mansion are some of the most under-appreciated collections in D.C.

An Industrial Revolution-era public work that purified water using nothing but sand.

An atomic bomb-proof strongbox protects the U.S. Constitution from terrorists and thieves.

This imposing Masonic temple a mile from the White House was the first public library in Washington, D.C.

The walls of the iconic dome are hollow and have a secret stairway.

A museum cafe showcases Native American dishes and indigenous ingredients from across the Western Hemisphere.

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.

With over 100 jam-packed rooms to explore plus elaborate tea services and events, the Mansion on O Street is a hidden treasure.

Home to items never before seen by the public.