The Tongariro River has cleved a deep ravine through the rugged volcanic terrain of the Kaimanawa Forest Park. At one point the high walls of the ravine close up on the river like giant pillars, forcing it through a narrow gap at high speed. You have to kayak through it to fully appreciate it but mountain bikers and hikers do cross the chasm on a scary 40 metre long suspension bridge high above the river.
The Pillars of Hercules Track starts by a busy highway on a dangerous corner with little parking space. You then ride about 5 km down an old 4wd track until come to the swing bridge and finally realise why you bothered! After the bridge there is about two kilometres of glorious singletrack as you go around the top of the gorge through a fine beech forest with the sound of the river below and the birds above. Then you'll reach the Urchin Campground (and toilet) where you turn around and go back the way you came for a total ride of 14km.
A better way to ride the Pillars of Hercules Track is to combine it in an 18km loop with the Tree Trunk Gorge 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. After that it's just a 2km ride down the busy highway back to Tree Trunk Gorge Road.
There is more on the Tree Trunk Gorge Track here: https://www.singletracks.com/bike-trails/tree-trunk-gorge.html
Description updated December 2017 by Jim Cummings