We would have loved to have taken on the Tongariro Alpine Crossing - a one day walk along the tops of the ranges, but this is not the easiest in winter and the woman in the alpine centre looked positively relieved that she didn't have to try and talk us out of it. In these conditions you need guides, full gear, crampons, picks etc. So instead we took this much easier (but still cold) two hour forest and waterfall walk.