The enormous 250-room Vanderbilt mansion conceals hidden doors and secret passageways.

A giant red chair bolted to a rock on a remote mossy hillside in Iceland.

This 1,300 year old monastery built atop a single rock was once only accessible depending on the whims of the tide.

A tiny church on a man-made island in the Adriatic.

These historic defenses ensured the city within would survive hundreds of years of occupations, sieges, and invasions.

"the sweltering inhabitants of Charleston and New Orleans, of Madras and Bombay and Calcutta, drink at my well . . . The pure Walden water is mingled with the sacred water of the Ganges."

One of two lighted lanterns hung in the church belfry on the eve of the Revolutionary War to warn that the British were on their way.

An isolated, rusty phone booth commemorates Iceland's first international telegraph cable.

This rocky spread has been squeezed up directly from the bowels of the earth.

A forlorn fishing village on the coast of Labrador, full of shipwrecks and Spanish gold.

An ancient Viking village in North America that predates Columbus by 500 years.

Largest Roman Catholic church in North America.

A lovely aquatic park built by a one-armed Civil War veteran who made a fortune from lotuses.

A hidden gem on the lawn of the U.S. Capitol Building designed by landscape architect Frederick Law Olmsted.

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

Enormous piles of historically significant stones, dumped by Congress in a forest, and abandoned for 60 years.

One of the dwarven trees dates back to 1625 and survived the Hiroshima bombing.

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

Home to items never before seen by the public.

The oldest building in the District of Columbia was preserved because of a mistaken connection to George Washington.

Iceland's largest lagoon is home to stunning multi-colored icebergs.

The unique waterfall in Iceland's south features a backdrop of geometric black lava columns.

Three columns of volcanic rock shoot out of the ocean.

Strange rock formations tower above the river that snakes through this enchanting Icelandic canyon.