This mountain bike route of 25miles adds a loop of natural trails into the middle of the Marin Trail. It uses part of the historic Sarn Helen trail to head south from the Marin Trail before a return leg below Moel Siabod. This extra loop has a mixture of forest tracks, rutted double track, bouldery descending and fantastic views.

1. Start from the Marin Trail car park (GR790609). Ride the first half of the Marin Trail. After the Dragon’s Tail continue following the Marin Trail for a little while to a crossroad junction with a tarmac lane (GR758579). This junction has a signpost ahead on the right pointing left to Nant BH and right to the Ugly House (Ty-hyll). Turn right and descend the lane to the Ugly House and a junction with the main road, A5, in the bottom of the valley (GR756575).

2. Turn left onto the main road and ride across the bridge. Directly after the bridge take the lane off to the right that follows the course of the Afon Llugwy. Go up the second forest track on the left for a short, steep climb to a crossroad (GR753573). Turn left and continue climbing past the forestry gate. This trail traverses the hillside and soon descends to a concrete stream crossing just before another forestry gate and a junction (GR758572).

3. Turn right at the junction and climb steeply for a while. At the next junction turn left, then a short distance later at the following junction turn right. Continue climbing to a long left hand bend at the top. Follow the forest track straight on across the top of the hill, then down a gentle descent. Eventually the trail bears right and passes a forest track on the right. Just after this is a forestry gate and a junction with a forest track on the left (GR769568). Go straight on and follow the track through a number of bends to the next junction. Turn right at this triangular junction and drop through a dip then climb a short way to the next junction, with a track on the right (GR773561).

4. Turn right to join the Sarn Helen trail. This starts with some bad tarmac as it climbs to a gate by a house on the right. Go straight on through the gate and continue climbing. The track then flattens off and comes to a junction with a gate on the left. Go past the gate and follow the track as is descends right then left to come out at a gate by some abandoned houses on the right (GR768555). Go straight on through the gate and climb the rocky trail in to the trees. The trail soon flattens off and undulates through a clear area in the trees. Follow the double track straight ahead, past a big rock wall on the right, to a crossroad junction (GR766551).

5. Go straight on up the rocky double track ahead. It soon flattens off and undulates across the top of the hill. There can be some sections of deep water on this trail and your feet could get very wet. The track eventually descends through a loose S-bend and comes to a gate. Go through this gate, and the next, to come out at a tarmac junction (GR759543). Go straight on and continue descending. Be careful when descending this lane as it is green in the middle, often damp and has blind bends. Near the bottom bear left, past a track on the right, to a junction with the main road (A470) in the bottom of the valley (GR753538).

6. Turn right and follow the main road to Dolwyddelan. On entering the village turn right up a small tamac lane just after the first couple of houses (GR738525). If you reach a footpath sign on the left hand side of the main road you have gone too far. For a good food stop go straight on to the junction in the middle of the village where there is a Spar with a covered outside seating area on the left. Follow the lane up between the houses for a very steep tarmac climb. Keep going straight on up the climb where it becomes less steep, rocky double track. The track eventually bears left up a tricky rock section. It’s a short but tricky section of slate bed rock covered in loose rocks, with water usually running down it. It's doable but far from easy. After the slate the track bears right over more loose rocks, then up a short but very steep section of tarmac to a junction (GR738527).

7. Go straight on and continue climbing, now up a shallow gradient. The tarmac soon gives way to a forest track and pine trees before coming to a junction with another wide forest track on the right (GR739528). Go straight then at the next junction bear left and descend to a small concrete bridge. After the bridge stay on the main track and climb past the tracks on either side before eventually descending to another concrete bridge. After the bridge go straight on past a track on the right to a three way junction just after (GR731544). Follow the sign pointing right to Capel Curig. At the next two junctions go right. This will bring you out to a gate at the edge of the forest (GR732548).

8. Go through the gate and along the rutted double track underneath Moel Siabod, on the left. After another gate halfway along the track, prepare for a few more puddles that will get your feet wet. Eventually the track descends through a couple of sweeping bends to a crossroad junction (GR737560). This is a good place to drop your saddle if you need to. Go straight on for a steep descent strewn with big loose boulders. After the main section of rocks bear left to a gate. Go through the gate and cross a steam, then complete the descent on a shorter section of rocks that finishes at a junction with a lane (GR736567).

9. Turn right on the lane and follow it along the course of the river, on the left, all the way to where it finishes at the previously visited junction with the main road, A5 (GR756574). Turn left and cross the bridge then turn right and go up the steep lane past the side of the Ugly House. Climb the lane all the way up to the crossroad junction with the signpost on the left (GR758579), to rejoin the Marin Trail. Turn right and follow the Marin Trail marker posts all the way back to the car park at the end of the trail.