There are three lovely beginner trails along both sides of the Waikato River - the Rotary Ride, Redwoods Track and the Aratiatia Damn Ride.
The track starts at the end of Spa Rd on County Road at the Spa Thermal Park and heads North on easy single track for 4km to Huka Falls. The Track crosses the Otumuheke Stream approximately 200 meter upstream from the Waikato River. From here the track meanders through gullies, twists around trees, runs alongside open farm land, crosses two streams via bridges, passes through culverts and has great views of the Waikato River and open valleys all the way to the Huke Falls. The Huka Falls are a spectacle of sight and noise as over 220,000 liters of water per second from the Waikato River is funneled quickly from 100 meters wide through through a narrow 15 meter wide gorge. The water falls in two steps (8 meters at the top and 11 meters at the bottom) creating a deafening noise.
From the Huka Falls you can cross over the river and head back to Taupo along the 2.5 kilometer Redwood Track which is also a gentle single track back to town on Huka Falls Rd. When Huka Falls Rd meets State Highway 1 there is a cycleway along the edge of the highway to avoid the traffic. Once you cross the control gates back into Taupo you cna head left and ride all the way along the river and Spa Rd back to the start of the Rotary Ride.
Alternatively continue on the Rotary Ride as it turns into a trail all the way to Aratiatia Dam some 7 kilometers away. Although this track starts with a bit of a nasty short climb it is an easy track thereafter suitable for most beginners. In the summer months (October to March) the flood gates on the damn open every 2 hours between 10am and 4pm - which is a pretty impressive sight. Head back the same way as you came to Huka Falls.
From the Huka Falls bridge you can also ride up to the Helistar Hub Cafe and a linking tunnel under the roadway to the Wairakei Forest with it's network of fantastic flowing trails.
A final warning - the trails around the Huka Falls are very popular with walkers and tourists so although they are wide enough to pass walkers while on your bike you need to be in the lookout.