Shallow then deep, all the way in then all the way out, real fast then super slow; jam your fist in then take it out and pump like there's no tomorrow, holding on for as long you can -- tube-riding is an atavistic and beautifully simple pursuit, albeit a fiendishly difficult one. Irishman Cain Kilcullen is a veritable demon in the barrel, as this short clip by Peter Martin makes abundantly clear. That final tube is about as deep -- and probably as shallow, for that matter -- as they come.