Enter the Beacon Theater from the side door tucked in a tunnel off West 74th Street, and you’ll find yourself in an industrial peach-beige space straight outta Welles’s screen adaptation of Kafka. Get in the rickety elevator, and you can visit the series of cramped dressing rooms and impromptu offices going three flights up. Or you can take a spindly staircase down into the labyrinthine ghost town beneath the stage. If you’re unlucky, the tour manager prods you through a tiny door out into the hall. But conversely, if you find your way through the maze, you can chill in the makeshift café directly under the place the Allmans’ drum risers are set up. Security’s always a bitch, but this odd, dreary backstage—structured at odd angles, like prime German Expressionist set design—can be the locus of divine rock and roll experience.