Just over an hour's drive west from Christchurch, up in the mountains is Craigieburn Forest Park. For a challenging half day ride, you can bike up the Craigieburn Ski Field access road to the ski field, then back down the valley to Lyndon Saddle for a great down hill ride back to the Craigieburn picnic/car park area.
An hours drive from Christchurch, the Wharfdale Track is very accessible, and offers a great challenging ride with fantastic scenery. You can choose to ride the single track through the Beech forest to the old Townsend Hut site and turn back and return the way you came, or carry on along the 4WD track to Lees Valley Road and back to Oxford via Ashley George Road. There is also the option to stay a night at the Wharfdale Hut.