Kirwans Track is a hiking trail that became available to mountain bikers a few years ago and quickly became something of a legend for it's tough upward slog and ruggedly technical ride back down.
It climbs over 1000 metres in 14km as it rises relentlessly through rain forest to Kirwans Hut high in the hills above Reefton. It's steep and the surface is sometimes soft, sometimes rocky, sometimes slippery, sometimes off-camber, generally challenging. There are many push-or-carry obstacles such as slips, tree falls, rock steps and washouts. All but the very fit and strong will do a lot of walking. Expect to take around four hours or more to reach the hut at the summit. You'll probably be in the clouds by then but if not you'll enjoy a fine view over the surrounding hills - lots of them.
You ride back down the way you came up and that's a ride that mountain bikers dream of. It's a long, looong way and ruggedly technical. It will take you over an hour not including stops to cross obstacles or just to rest your brake fingers.
The downhill ride has gained such a reputation that it's not unusual for riders to skip the slog up with a helicopter lift.
There is drinking water and a toilet at the hut.