This Florida sinkhole hides a rainforest-like micro-environment in its depths.

The former home of the Nobel Prize-winning American writer is now home to dozens of six-toed cats.

A haunted hill that supposedly defied gravity.

A mysterious castle built as a monument to lost love.

The only swimming pool listed on the National Register of Historic Places is emptied and refilled each day with naturally filtered water.

Despite its lavish ornamentation, and wholesome lifestyle of its devotees, this mountain commune has faced its share of issues.

A hidden passageway now marks the site of an assassination attempt on Ronald Reagan that some say broke a 140-year-old curse.

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

There's an old indoor swimming pool hidden directly underneath the White House Press Briefing Room.

Architecture lovers won’t stop touching the National Gallery's 19.5 degree marble prow.

This sandwich shop has a century-old elevator behind a sheet of plexiglass.

This stunning blue and gold room changed cities twice before becoming part of the Smithsonian.

A haunting tribute to pioneering photographer Clover Adams.

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

The first purpose-built art gallery in the United States is once again open as a center of craft arts.

The country's oldest continually-operated mini golf course lies hidden in plain sight, eclipsed by one of D.C.'s most popular tourist attractions.

A tiny piece of the Moon is embedded in this stained glass masterpiece.

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

Everyone's invited to put on a miniature concert with this world-class musical wonder.

This secluded walking trail is a hidden gem of a Pittsburgh park.

There are more than 4 million bricks inside this unofficial Lego museum in a former middle school.

Small, privately owned island divided between Michigan and Ohio with abandoned vacation homes and a derelict lighthouse.

Take a drunken tour inside the world's largest known geode.

One of Detroit’s oldest blues clubs stands in defiance of the passage of time and the city’s shifting fortunes.