From the car park, climb the stairs up to the level of the former railway line. Turn left to head south across the bridge over the road. Continue along the railway path for 800 metres (half a mile) to reach the summit tunnel, then turn and retrace your steps. It's quite safe to walk through the tunnel but you'll need a torch.    Or from the car park walk up the gentle ramp away from the road (northwards), soon to join the railway path. Continue for as far as you wish, then turn round and retrace your steps: after 2.8 km (1¾ miles) you'll reach a tunnel, which is safe to walk through with a torch. On the return to the car, if you find yourself crossing the bridge over the road, you've gone a few metres too far.