The Tree Trunk Gorge Track traverses a beautiful beech forest in the rugged terrain of the Kaimanawa Forest Park. The trail is rough, rocky and it's boggy when wet. Most riders will do a bit of pushing here and there. There are river crossings. They are non-threatening when not in flood but you will get wet feet.
The Track starts near the bridge over the Tongariro River on the sealed Tree Trunk Gorge Road. It then undulates through the forest above the gorge for about 5km when it meets Kaimanawa Road at the Urchin Camp Ground. That's where the Pillars of Hercules Track starts. For a description of the Pillars of Hercules Track cut and paste this URL into your browser: https://www.singletracks.com/bike-trails/pillars-of-hercules.html
The best way to ride the Tree Trunk Gorge Track is to combine it in an 18km loop with the Pillars of Hercules Track. Park just off the Desert Road on Tree Trunk Gorge Road. Ride down Tree Trunk Gorge Road, then the Tree Trunk Gorge Track, then the Pillars of Hercules Track which takes you back up to the Desert Road. Then it's just a 2km ride down that busy highway back to Tree Trunk Gorge Road.