O n a stretch of White Plains Road, three or four blocks from the Allerton Avenue train station in the Bronx , there once stood a building that pulsed like a second heart for New York City’s hip-hop generation. To the untrained eye, it was just another low-slung commercial structure tucked between storefronts and fast-food joints. To the five boroughs, it was church, school, battleground, talent show, and safe haven all at once — an iconic skating rink called Skate Key Roller Rink. If you grew