There are several great mountain bike tracks to ride on either side of the Waikato River between Taupo and Huka Falls. The most popular is the Rotary Ride to Huka Falls. From Huka Falls, you can can cross the bridge and spin back down stream to Taupo on the Redwoods track.
Alternatively, you can continue down valley to Aratiatia Dam (see Aratiatia Dam Loop). There is also a good single track linking Huka Falls to the Wairakei MTB tracks.