Like most North Island bike parks, Kohitere Forest is set on steep hills in a plantation pine forest. To get to the top you can ride up Trig Track. It's wide, well-surfaced and very popular with walkers and runners. It's a granny gear grind all the way up . You should reach the top in under an hour. Alternatively you could go up on Kurt's Track, a testing grade 4 singletrack. The most popular way to come back down is on a track called "The Edge". That's a grade 4 track that goes down steeply but it's more like a descending cross-country track than a classic downhill track.
The Gardner Track is a longer way down. It doesn't have great technical interest although navigating some of the rutted switchbacks will get your attention. It's grade 4.
There are a few other tracks including some on the other side of the hill. There are also a few forestry roads that people ride on. In general the singletrack in this forest tends to be steep, rutted in places and very old-school. It is very slippery when wet. It tends to stay wet for a long time after rain and it rains here often!