Like alligators in the sewers, the homeless people living in the train tunnels under Manhattan are a kind of urban myth now. The novice documentary filmmaker Mark Singer moved in with them and together they made a sleeper hit called "Dark Days" that exposes their troubled, introspective, and strangely compelling lives. There was a whole neighborhood under there: a filthy shantytown with electricity and running water courtesy of the city of New York. It was a place dozens of people called home for years before Amtrak evicted them. Mark Singer was 17 when he left his home in London to model in the Big Apple and instead fell in with a group of drug-addicts and social outcasts who won him over with their endearing personalities and humbling ability to survive. Mark Singer sold everything he owned, maxed out credit cards, and lost his own apartment to help his friends get out of the tunnels.