There is a purpose built sleding area up there just past the first chair lift on the Whakapapa side. You walk there & it's free. Not to sure on Turoa side but I'm sure they'd have the same.
ETA: check out how much it is to hire sleds from Ocean & Ice.
Take thermos of warm milo to warm yourself up afterwards

Plus lots of spare warm clothes.
Edited by AandCsmum