The walls of the iconic dome are hollow and have a secret stairway.

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

The country's oldest continually-operated mini golf course lies hidden in plain sight, eclipsed by one of D.C.'s most popular tourist attractions.

Fittingly, America's museum of architecture is itself a magnificently designed old building.

The site of the climactic scene from the classic horror film is now a historic landmark.

The United States Capitol's former columns still stand.

A tiny museum housed in a New York freight elevator specializes in the "overlooked, dismissed, or ignored."

A Yiddish theater turned movie house turned rock and roll landmark turned gay disco turned bank.

The tiniest little stage in New York.

There must be a pun in this haystack somewhere...

A historic 1890s architectural masterpiece with an iconic clock tower that, once open to the public, now faces an uncertain future.

The oldest operating apothecary in the US has treated everyone from Thomas Edison to Mark Twain.

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

Elevated freight railway turned wildly successful urban park.

A terrific purveyor of natural history objects and curios.

An uber-secure, windowless tower of doom in the center of Manhattan is an NSA spyscraper.