The Lewis Pass area has truck loads of thermal springs, making it a crash hot destination for winter mountain biking. A classic trip is to zip up to Hurunui Hut in the Lake Sumner Forest Park.
The action starts at Lake Taylor, 40km inland from Hawarden in North Canterbury. Unless you have a stroppy 4WD you'll need to park up at the south end of the lake. There are no major hassles with security here. The grassy flats on the lake shore make for great camping but it can blow like hell and beware of mega frosts in the winter.
This trip works best as an over-nighter at this time of the year - letting you make a late start and early finish to avoid the coldest part of the day. Head around Lake Taylor on the 4WD track until you get to Loch Katrine (625m), then drop down to HomeBay on Lake Sumner. Long and wide grassy flats lead to the NZFS No. 2 Hut (imaginative names) at the edge of the Beech Forest. You're about 12km from your starting point and getting closer to the source of the Hurunui River. Stay on the true right(ie. right as you face down stream) of the Hurunui and follow the vague bulldozer track to the newish Hurunui Hut - a modern 20 bunker on the manuka terrace above the river opposite Dinner Hill.
Stash your overnight kit, grab your towel, shower cap and make directly for the hot pools. You'll need the map to find them - X marks the spot just up the hill and above the track. It's about 30 mins by bike then another 15 mins on foot to the pools. Your nose will tell you when you're there. It's a wild setting in the bush and there's room for up to 10 bods. Retrace your steps before darkness falls and everything turns to custard - or arm yourself with a fancy torch. From the Hurunui Hut it's back out the same way you came in.
A diversion for the more adventurous is to continue over the Kiwi Saddle to the Hope Kiwi Lodge. From there you can in theory ride down the Hope River to the Lewis Pass road - but you need to get permission from the land owners at Poplars Station first.