A commemorative plaque hides a door that leads down to the New York Public Library's underground book bunker.

The former home of the reclusive "Weird Wendels" who dominated New York real estate a century before Donald Trump.

A grand New York post office that is home to mailman Santas, scraps of postal history, and a pneumatic mail system.

A three-story copper skybridge connects two Manhattan buildings with Art Deco luxury.

The summer home and later final residence of acclaimed American sculptor Augustus Saint-Gaudens.

One of the U.S. Forest Service's only mansions is outfitted with a dinner table for floating food.

The largest known open fault in the United States is basically a giant natural refrigerator.

This grand gothic brewery has been pumping out suds for over a hundred years.

This pirate-broadcasting-tower-turned-restaurant played a rebellious role in the history of Dutch television.

This once-private estate is now a dreamy, meditative garden that's open to the public.

A mammoth pair of Civil War artillery guns abandoned out in the forest.

The 72-foot giant escaped confinement in a large patch of mulch only to be reburied in the sandy shores of the Potomac River.

A rotating cast of guys and dolls in front of a Washington, D.C. building.

The final residence of an educator, civil rights leader, and presidential advisor was also the first headquarters of the National Council of Negro Women.

The sculptor was instructed to add “stallion attributes” to the general's bronze mare.

A bas relief commemorates the "Nuns of the Battlefield" who cared for soldiers on both sides of the conflict.

Railroad officials in the early 1900s sought to spare travelers the sight of Roman soldiers’ private parts.

This sprawling art park is filled with sculptures, nature trails, and art workshops.

The first American home of the isolated, egalitarian religion has a trove of Shaker architecture and artifacts.

This tiny church near Sleepy Hollow contains Henri Matisse's last work, a rose window, and nine windows by Marc Chagall.