Originally conceived as part of a proposed Arizona State Capitol building in the 1950s, this structure built in 2004 stands as a monument to the architect's legacy.

A replica of the flagpole that gave a frontier town its name.

Eons ago, a rushing lava river formed this pristine passage through solid rock.

A working cattle ranch with remarkably well-preserved prehistoric petroglyphs and ancient ruins.

America's only nuclear missile silo open to the public.

A reproduction of earth's many biomes.

In a 345-million-year-old cave that's 200 feet underground, dinner awaits.

This 4,000-foot-diameter hole is touted as "the most well known, best preserved meteorite crater on Earth."

A geological mystery on Camelback Mountain.

This monumental fountain has moved around the city multiple times.

A master of trompe-l'oeil creates a stunning, tourist-fooling dome out of a flat ceiling.

This hidden Art Nouveau courtyard is an opulent feast for the eyes.

A forgotten "city of water" underneath the famous Trevi district.

This Route 66 classic sports a giant fiberglass rabbit that you can ride.

Witnessing the might of this dessert-colored desert waterfall is a rare, powerful treat.

A 98-room castle in the middle of Toronto that bankrupted a 19th century electricity multimillionaire.

Lost subway station nestled beneath Toronto's busy commuter line.

This stately mansion, built in 1787 by America's first Secretary of the Navy, is rumored to be one of the most haunted buildings in Washington, DC.

Look closely and you’ll notice that the color changes a third of the way up the tower.

This seemingly out-of-place gas station by the Watergate hotel was once described as the most expensive gas station in the world.

This nine-story building is the oldest standing skyscraper in D.C.

This unacceptably tall building was the real reason for Washington, D.C.'s skyscraper ban.

Legend has it that President Grant’s frequent drinking in the lobby gave rise to the term “lobbyist.”

A little marble compass above George Washington's (empty) tomb in the Capitol marks where D.C.'s four quadrants intersect.