An underground city of salt.

A small plaque promises cold, hard cash in exchange for work by the famous pop artist.

The headquarters of one of the world’s longest-running humor magazines bears a noticeable resemblance to a head wearing a Prussian helmet.

Dedicated to the neverending mathematical constant, this plaque next to a park bench was sponsored by an anonymous benefactor.

Malcolm X's house during his most formative years faces an uncertain future.

This historic Boston building has gone from personal estate to porn theater and back again.

The oldest working bell set in North America, the bells at Old North Church sat silent for their first four years in Massachusetts.

The site where Charles Dickens gave his first public reading of "A Christmas Carol" in the US.

This landmark cemetery in Boston was created more than 300 years ago.

Narrowest house in Boston.

Beautiful steampunk ghosts of early Massachusetts.

One of the now-less-hidden floral gems of the "Emerald Necklace."

Two hundred tons of pioneer artifacts were painstakingly recovered from a shipwreck at the bottom of the Missouri River.

When the rain falls, this drain system turns into a musical instrument.

Perhaps the oldest vine in North America, this sprawling plant helps make a sweet wine.

Menacing or in memoriam, the Silent People and their meaning are left to interpretation.

At more than 5,000 years old, these structures are among the oldest free-standing stone buildings in the world.

The largest Art Nouveau complex in the world is a Barcelona hospital with a 600-year-long history.

Stone slabs along the coast warn of Japan's tsunami-ravaged past, often marking the highest point of a wave's reach.

This retro diner claims to be the birthplace of poutine.

A historic structure that once housed pigeons used by farmers to help fertilize farmland.

A multiversal transit station located right below a highway interchange.

An immersive environment that is part haunted house, part choose-your-own-adventure, and part jungle gym.

The awe-inspiring ship from the golden era of cruising has an incomparable history and a reputation as one of the world’s most haunted places.