Here is a place I have trekked some time ago but revisited recently and did a survey of a possible future trip.
Here is a future ultimate extreme mountain bike experience. There are two options-
1. Park at Sinipsip, then ride to Bakun for an overnight stay and return to Sinipsip the next day. Its 34 kilometers of mountain off road.
2. Park at Acop toll gate, then ride or take a bus/jeep to Sinipsip. Ride to Bakun for an overnight stay. Then ride to Kibungan then Kiangan and then to Acop toll gate for the ride back home.