You have to be a little crazy to get into XC skiing, but you have to be full-on nuts to session a terrain park in spandex, soft boots and skate skis. A crew of Norwegians at Oslo Vinterpark, Tryvann did just that, stomping front flips and backflips, slicking rails and boosting above the lip on the hill’s halfpipe. Norwegians, apparently, love their XC skis.