Dark Days is a documentary made by Marc Singer, a British filmmaker. The film follows a group of people living in an abandoned section of the New York City underground railway system, more precisely the area of the so called Freedom Tunnel. When he relocated from London to Manhattan, Marc Singer was struck by the number of homeless people he had seen throughout the city.

Singer had befriended a good number of New York's homeless and later, after hearing of people living underground in abandoned tunnel systems, he met and became close to a set of folks living in The Freedom Tunnel community stretching north from Penn Station past Harlem.

After living with them for a number of months, he decided to create a documentary in order to help them financially. The film's crew consisted of the subjects themselves, who rigged up makeshift lighting and steadicam dollies, and learned to use a 16mm camera with black & white Kodak film.

Singer himself had never been a filmmaker before, and saw the production of Dark Days as a means of gaining better accommodation for the residents of the tunnel. The post-production process took years, as financial difficulties created delays, as did Singer's insistence of creative control to protect the tunnel residents.

The film features music by DJ Shadow, including excerpts from Endtroducing... as well as his album with U.N.K.L.E. Melissa Neidich was the editor of the film. Cinevision, a New York City camera shop, supplied Singer with cameras for the two-and-a-half years of filming. When Singer ran out of money for film, Kodak supplied free damaged film for the project.