One of the few remaining monuments dedicated to South Boston's Irish heritage.

The strikingly modern structure stands out among the brick buildings speckling the Harvard Business School's campus.

Mrs. Mallard and her brood are a beloved fixture in Boston Public Garden.

Ice cream stand, snack bar, and time capsule of milk conveyance.

Narrowest house in Boston.

Ralph Waldo Emerson spent two years living here decades before it became a Frederick Law Olmsted-designed park.

One of the oldest used bookstores in the U.S. has been selling antiquarian treasures since 1825.

This upscale streetwear store is hidden behind a fake Snapple machine in the back of a deli.

An enormous, inside-out glass globe built in 1935.

A drab two-story office space in Delaware is a hidden tax haven for Hillary Clinton, Donald Trump, and over half the Fortune 500 companies.

Hundreds of antiquated typewriters and office machinery show the technological evolution of business.

This collection of odd proofs of concept is like taking a walk through the imagination of a Victorian engineer.

It's not hard to see why the historic Peabody Conservatory of Music's library has been described as a "cathedral of books."

Daily lunch spot for many of Washington, D.C.'s cab drivers.

For 60 years, the academy had no permanent location until members voted Washington D.C. as its forever home.

Architecture lovers won’t stop touching the National Gallery's 19.5 degree marble prow.

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

The towering figures were created from the cemetery's fallen old-growth trees.

The Byzantine, pre-Columbian, and medieval art at this stately mansion are some of the most under-appreciated collections in D.C.

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.

A three-story tower of books about Abraham Lincoln is one of the more unusual monuments to the president.

A wondrous old library overlooking the nation's capital.

With over 100 jam-packed rooms to explore plus elaborate tea services and events, the Mansion on O Street is a hidden treasure.

Franciscan monks created a facsimile of the Holy Land for North Americans who couldn’t afford the trip overseas.