The only urban monument in the world designed by the great surrealist painter Salvador Dalí.

Rising from the sea like a stone monster.

Where beautiful signs live on forever.

Rome's semi-secret peephole vista is also a former Crusader stronghold.

Sleep snuggled in a sphere suspended atop the forest canopy of Vancouver Island.

The largest permanent Monopoly board makes one of the longest games even bigger.

Hidden beneath a bridge, this waterfall is known for the large amounts of graffiti painted on its base.

A whimsical village of unique treehouses resides in a Washington forest.

The second largest waterfall by volume in the U.S., Willamette Falls is outdone only by Niagara in the amount of water that is pushed northward.

This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

A dozen U.S. presidents have stayed at the historic resort, which was known as James Buchanan’s “Summer White House” from 1857-1861.

The doodles of a genius line the walls of a secret room under the Medici Chapel, where they were hidden for nearly 500 years.

The vast chamber inside this abandoned cooling tower looks like something out of a sci-fi dystopia.

An unfinished tomb carved into a giant boulder in the Arabian Desert.

A vortex fountain that seems to rise out of the ground.

An isolated 17th-century chapel on a remarkable site once dedicated to Celtic sun worship.

The entire length of the border is marked by a 20-foot-wide slash through the trees.

This iconic L.A. bookshop is housed in an abandoned bank—both symbolic and chic.

The sound of swaying stalks in this stunning grove has been named a governmentally recognized sound.

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

A winding path built in secret on the edge of the continent.

This semi-secret storybook hedge maze is also the oldest garden in the city.

A room in New York City that contains 250 cubic yards of dirt worth a million dollars.

A beautiful but toxic fountain of mercury.