Beneath the southern end of the Golden Gate Bridge is the “Gibraltar of the West Coast,” a fort built to protect the San Francisco Bay from naval attack.

At the base of the Golden Gate Bridge, a small sign basically begs for a high-five.

These subterranean storage areas hold emergency water reserves.

The second building of its name to occupy this location might be the finest flatiron building in San Francisco.

An unassuming secret door once led to a legendary watering hole.

Tucked away amidst some of the most famous addresses in the world is New York’s only fraction of a street.

Amid the marketing blitz of modern Times Square is an elegant holdover from its showbiz glory days.

This mosaic dedicated to John Lennon was tended for years by a Beatles super-fan.

This historic address is home to the beloved ball and is an almost totally empty building among the most expensive real estate in the world.

This sculptural piece by the artist Tom Otterness doubles as a jungle gym.

A whimsical, but often overlooked clock in Park Avenue.

A trove of century-old litho stones from the Puck Building's printing days were discovered behind a cellar wall, and are now hanging in the store.

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

This translucent sculpture represents a quintessential component of New York City's skyline.

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

Hidden in plain sight on a pair of Manhattan subway tunnels are a pair of public instruments that sing to each other.

Named the fifth most beautiful building in America in 1885, this former courthouse boasts the best view in the Village.

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

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

The 28-foot granite map plots the locations of 40 theaters in New York City.

This too-low North Carolina railroad trestle is still a notorious big rig executioner.

This sculpture of a fisherman spent six years at the bottom of the Schuylkill River.

The artist and New York City icon lived, worked and died in this converted carriage house owned by another iconic artist, Andy Warhol.

This wall on a street corner in Lower Manhattan has been a blank canvas for a rotation of renowned artists since the 1980s.