From downtown Nelson go up Maitai Road for 2km, then turn left into Sharlands Road where you'll see the car park in just 50 metres.
There is a map board in the car park. Check it out then treadle your way up gravel forestry roads towards the top, 500 metres into the sky... You go up Sharlands Road and then Bobs Fern Road (it's a loop and you want to go up it the second time you see it). Before long you'll see a sign to the Scottwood Wiggles trail. I think there are three signs and three ways to get onto this sweet singletrack at different levels. ---
You can go all the way up the road to a fire break which you can push your bike up to the very top of the hill. From there you can take a trail called Slingshot which goes down you to the start of Scottwood Wiggles. But don't! I did and it's not worth it. The locals obviously don't bother - it's overgrown and little used. ---
During the descent, Scottwood Wiggles morphs into Sharlands Valley Trail but you don't need to know it. Just keep following your front wheel. The only time you come out on the road, turn down left then within 20 metres turn right into more singletrack.
The trail down is suitable for intermediate riders. It's varied and interesting, mainly through pine forest, but don't expect lots of fun stuff like berms, jumps, rollers and on it. But it's a very pleasant down-slope ride that will well reward you for the long slog up the hill. ---
Other trails you could try are Ching's Highway and R&R Rush. I didn't so it's up to you to review them! ---
If Sharlands Road is closed because of logging operations then I think your best option is to go to another mountain bike park such as Codgers which is not far away. ---