“Nightmare: New York”, staged in a Lower East Side building, depicts the ugliest, scariest vision of 1970s- and ’80s-era Gotham. Subways are awash in graffiti, creeps and crime. Menacing punks roam the streets. And the “characters” of Times Square don’t look anything like Elmo or SpongeBob SquarePants. Visitors wander through a 13-section maze of New York’s dark side, starting with a blackout, followed by scenes amid flashing strobe lights or a fire. Characters include a psychotic, Son of Sam-style serial killer, a urine-stained homeless man, a deranged woman crawling on the floor and tunnel-dwelling “mole people” whose grotesque faces suddenly pop up from dark corners.