I’ve written a heap about Woodhill and Rimmers over the years, about my disillusion with the inaction and neglect of those nominally maintaining the walking tracks and so on. I’m consigning that to a linked history section and revisiting the walks for an up-to-date assessment.
There are two official walking tracks at Woodhill, the Short Loop Track and the Long Loop Track.
I’m going to add a couple more: the Short Short Loop Track and the Long Short Loop Track.
In fact, depending on the use you make of the myriad horse tracks and quad bike tracks and forestry roads, there’s no limit to the routes you can devise. The BMX tracks, though, are totally off limits. Bikes, being silent, ridden by complete lunatics, and considerably faster than pedestrians are bloody dangerous to be around.
As a destination for walkers, Woodhill has, sadly, come down in the world in recent years. Unless you are strongly attracted to pineforest and pampas grass, I recommend you go somewhere else.
5 years ago, it was possible to park one’s car and within 5 minutes be surrounded by native bush. These days, you are obliged, on threat of towaway, to park way, way down at the BMX base, and you have about 30-40 minutes of uphill walking through pine forest and pampas to reach the Nature Reserve. In the reserve itself, the easy open walking track of a few years ago has been neglected badly, and much of the track through the reserve is now crossed by fallen timber or encroached on by scrub from either side. The reserve also suffered considerably during the 2008 dry spell, and is still somewhat in recovery mode.
To get there, turn off SH 16 into Restall Rd, about 12 km south of Helensville, just south of Woodhill School. Follow the road for about 1.5km until you reach crossroads. Two of the roads are gated, and you turn to the right down Boundary Road for another kilometre or so until you reach the BMX carpark on the right. On the map below, one square = one kilometre

Available walking tracks are as follows:
Short Loop Track*

*This is a modification of the original Short Loop Track. In the NW corner, at the point marked X, the original track heads off for a protracted detour through pine forest rejoining the outward track at Y. At this point of the walk I have usually more interest in getting back to the cold beer in the van fridge, so I turn right down Selwyn Rd, and across to Walker, following the boundary of the cutover forest, and back along the outward path. For those who are curious to learn more about the interior of pine forests, I shall publish a short account in the weeks ahead, but I shall be doing it for completeness, no other reason..
Short Short Loop Track

At the point marked X, turn right off the Short Loop Track to return to parking area.
Long Short Loop Track

In the NW corner, at the point marked X there is a T junction. To the right is the basic Short Loop Track route. To the left is a portion of the Long Loop Track through native bush, and a number of experimental native plantings by the old Forest Service, well worth a 30 minute detour, though it can be a touch overgrown, depending how much recent love has been bestowed on it. Rejoin the original short loop track at Y.
The Long Loop Track
This is still to come. I’ve walked bits of it at various times, mostly as short extensions of the Short Loop Track or side expeditions off Coast Rd, or just exploring.
As far as I can gather, the extended portions of it are mostly used by horses or quad bikes, with releatively few pedestrians finding the prospect of extended pine forest walking even slightly attractive. You do get a decent walk along an isolated bit of coast, but that’s much more accessible — and interesting — further north.