This elaborate estate contains a stunning marble aviary, a sunken conservatory, and a magnificent music room with a two-story pipe organ.

Once adorning a New York skyscraper, these reclaimed ruins now haunt an Indiana park.

This hidden stream beneath Indianapolis makes an appearance in the best-selling novel "Underground Airlines."

A cablecar-station-turned-revolving restaurant with 360-degree views of the Swiss skyline.

England's steepest street has such a drastic incline that locals tie their parked cars to lampposts when it gets icy.

Rare wooden escalators lead deep down into an otherwise staggeringly monotonous tiled tunnel.

This ancient goddess temple inspired the design of India’s Parliament House.

This 170-year-old Swiss guesthouse built into the side of a mountain is best accessed by a cable car.

An abandoned railroad tunnel is now filled with bioluminescent bugs.

Clap your hands at the base of the pyramid, and the song of a sacred Mayan bird will echo through the air.

The remains of a magnificent medieval fortress that was the capital of a vast empire.

These ancient sunken lanes were naturally tunneled into the soft ground by countless footsteps.

The sixth of London's "Magnificent Seven" cemeteries, and a source of unlikely inspiration to Beatrix Potter.

Crumbling ruins of the thermal baths that once attracted royals and aristocrats from throughout Europe.

Swedish mice can dine at the Nuts of Life restaurant or take a date to the amousement park.

A mysterious monument where a woman who records say never existed was burnt alive for being a witch.

A scandalous Art Nouveau collaboration that set Paris all atwitter at the turn of the century.

A climbing route in the mountains of Italy’s Dolomites, built for soldiers during World War I.

This mysterious underground cave in Shropshire dates back to the 18th or 19th century.

This dramatic landscape hidden on the Isle of Skye looks as though you've stepped into the magical realm.

Fonts are born and bred here at the oldest letterpress type foundry in the United States.

These blingy, baubled skeletons lie in glass boxes inside a baroque Bavarian church.

A Yale University president wears full samurai garb in one of America’s oldest cemeteries.

A historic London pub with prison cells in the cellar and a "spy room" on the second floor.