This film features bloody knuckles, all-out grunt sessions and willful participation in pain. Welcome to the world of off-width crack climbing, a sub-genre that attracts a rare breed willing to jam elbows, knees, torsos — whatever it takes, really — into large cracks for climbing ascents. It’s painful, tough and occasionally downright awful. But two British climbers, Pete Whittaker and Tom Randall, love it.