A stone arch leads to a cavernous 1930s spring house tucked away in the Pennsylvania woods.

The oldest surviving synagogue in New York City is now a soaring art space.

Stripes of flowers bloom each spring in a 50 acre rainbow of color.

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

A house carved into a rock in the 1940s.

Trails through lava-carved tube-caves display sparkling bacteria and a rich history.

Remnants of a Victorian garden feature sitting in public woodland.

This lake in the Cascades lives up to its name, disappearing down a hole every spring.

"Respectful to the dead, safe and sanitary to the living, dedicated to the Genius of Memory..."

Canyon walls shrouded in ferns.

A 300-yard long natural tunnel runs through a ridge deep in the Appalachian Mountains.

Perfectly preserved ancient monastery in an impossibly dramatic location on a rocky island in the Atlantic.

The eerie remnants of an ancient forest were hidden under the sand for centuries.

An essential stop before plundering, BYO Cutlass.

Breathtakingly blue walls shimmer inside the "Glacier Behind the Town."

Experience park where visitors are told to expect the unexpected.

Northern Ireland's Brobdingnagian stepping stones.

A tiny red pebble marks what may be the quietest outdoor spot in the United States.

This 700-year-old street food market features baby octopus and soy donuts.

An ancient Scottish rock formation said to be the gravesite of a giant remains ensconced in legend and intrigue.

An abandoned castle owned and ignored by Masons carries a cursed history.

European castle ruins in an American state park are actually the product of death and grief.

An enormous park-like oasis, full of famous Chicagoans' graves.

Collapsing castle on the Hudson river was once the storage site of military surplus business.