Mother Nature outdoes herself with this stunningly beautiful set of caves carved into marble.

The remnants of two World's Fairs are here, complete with a 12-story globe, a mini-Manhattan, and a UFO-shaped pavilion.

A network of concealed passageways lies within a busy London Underground station.

Japanese national treasure originally built in 593 CE.

The gloomy ruins that inspired Bram Stoker to bring Dracula to life.

A restored Pittsburgh house of God has been converted to a marvelous house of suds.

These towering spires and glowing walls are carefully crafted from hundreds of thousands of icicles.

An uber-secure, windowless tower of doom in the center of Manhattan is an NSA spyscraper.

The fanciest public restroom in New York City boasts fresh flowers, art, and a classical music soundtrack.

The world's largest mountain carving could fit all of Mount Rushmore inside it many times over.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

Designed by Buckminster Fuller, this relic of the 67 Expo survived fire and ice.

The first park built over a freeway is a brutalist masterwork.

Nonprofit art center that promotes outsider, intuitive, and self-taught art.

A hidden beach at the end of a tunnel of mangrove trees.

A well-preserved Ancestral Puebloan ruin tucked beneath a desert cliff.

An Aztec snake god has taken the material form of an apartment complex.

The ruins of a Duke's bucolic dream, where camels once roamed alongside "Dutch" windmills and faux-Italian vineyards.

The ruins of this gorgeous clifftop castle look like something from a fantasy novel.

This hidden green space is the city's second largest conservatory.

During the holidays, a vintage subway train whisks New Yorkers back in time.

Legends surround this jagged rock formation in the New Mexico desert.

This massive redwood tree has a hole in the base big enough to drive through.

The world of the ancient Celtic civilization explained through a bewitching 11 acre garden.