From the Knoll Ridge Cafe it is about a 5 hour return trip via one of two unmarked routes. If you are unfamiliar with the mountain, check with DOC in the village and be very aware that in mist it is possible to lose the route especially in winter.
This is the highest mountain in the N Island, and subject to full alpine conditions even in summer. The routes cross lahar paths and there have been (rare) incidents of sudden eruptions occurring in Crater Lake without warning. In winter conditions, cloud and snow can lead to zero visibility 'white outs' making navigation hazardous and difficult.
High elevation, steep climb. Use a GPS or a map and compass if you are skilled at using them.