That trail is an old road used only by a few villagers. Now its famous to cyclists and enduro motorcyclists.
Or if you are going to Borneo someday, I heard the local bike tour follows the same trail. Not sure if uphill or downhill though.
Ignore the blue line on top from Tamparuli to Sinalau Bakas. If you can spot it, there is a straight but bendy road from Tamparuli to Sinalau Bakas, that is the actual trail.
Oh ya, sod that 4 meter wall I said earlier. I meant to say 4 foot.