Hundreds of prehistoric stones, arranged in perfect lines in a French field.

One of the most popular megalithic sites in Ireland stands as a humbler version of Stonehenge.

Every equinox this Maya pyramid puts on a spooky ancient light show.

No telescopes, no power, no gift shop: The Observatory of Chichen Itza, one of the world's oldest observatories, takes astronomy back to basics.

Native Americans built this circle of stones, which was used to predict astronomical events.

This hunter-gatherer architecture is believed to be the oldest religious complex known.

The ancient tomb acts as a calendar that keeps perfect time.

The largest earthwork effigy in the world.

The largest Neolithic ruins in the world hide a notably clean prehistoric metropolis.

Grotto replete with mystical designs laid out in glued shell mosaics.

The oldest bibliophilia club in America, with exhibitions on historic books and graphic arts.

Slyly buy a shake in the Parker Meridien lobby.

Blighted Irish field and the ruins of a 19th-century cottage on the edge of urban Manhattan.

Once considered the height of medical modernity, this structure is now the oldest remaining component of Roosevelt Hospital.

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

The oldest surviving synagogue in New York City is now a soaring art space.

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

Once the tallest building in the world and the site of "the highest dinner ever held in New York" this building now holds the most expensive penthouse in the city.

This ruined fort hidden at the top of Central Park can't seem to keep from losing its historical plaques.

Failed state-supported institution meant to rehabilitate students with intellectual disabilities.

The haunting, dilapidated remains of a former poorhouse on Staten Island's Greenbelt.

Once America's longest-manned military fort, now an abandoned hulk.

The name of this famed hospital was once a byword for the horrors of medical and psychiatric care.

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