Through Geological Time in the Avon Gorge

1 A noticeboard near the car park shows two waymarked trails, one of which, the Purple Trail, is being upgraded to wheelchair-friendly smoothness. This walk links parts of the two trails with the riverside walk along the famous gorge.

2 Start from the noticeboard on the Red Trail. This begins as a wide gravel path towards the river. After 50yds (46m) a sculpture on the left has been chain-sawn out of a tree: it portrays a mattock, a tool for hacking the ground. Here the trail bears right. In another 90yds (82m) turn left on the Red Trail as the Purple Trail continues ahead.

3 The wide path runs under beech trees, past a shelter that is roofed with shingles (wooden tiles). At a T-junction, with a bench, the trail turns left, heading up along the rim of a wooded combe. It bears right, into the combe, and turns along its floor for 200yds (183m). The trail then turns left on to a terrace path with glimpses of the river below. The sound that could be the roar of the Avon's rapids is in fact the traffic on the A4 on the far bank.

4 After 300yds (274m), at a point with a view ahead along the river, the Red Trail bears right on a smaller path past a picnic table. It slants down across a shallow combe and reaches a T-junction. Here, where the Red Trail turns uphill, turn down, following blue markers. These indicate a cycle trail. At its foot is the River Avon, where you turn right - your route now follows the Avon upstream on a wide riverside path for 1½ miles (2.4km).

5 Geological studies are distracted by the impressive Clifton Bridge, now almost overhead. Some 130yds (118m) before the bridge a rock-buttress opposite is studded with metal pins to stop it falling on the A4. Here turn off to the right, passing under a railway bridge numbered 19. A small and rather rough path goes up the floor of Nightingale Valley. Here you may feel with your feet a practical consequence of shifting from the Devonian to the Carboniferous: the limestone bedrock forms a particularly sticky sort of mud.

6 At the valley top a kissing gate ahead leads out on to a street; a left turn in this street would take you out on to the Clifton Bridge (¾ mile, 1.2km). Alternatively, the Blue Trail on the right can provide a quick return (¾ mile, 1.2km) to the car park. However, our route turns sharp right before the gate, on to a path marked 'No Bikes'. This runs alongside the drop into Nightingale Valley on the right. It passes through the earthworks of Stokeleigh Camp, to reach a viewpoint overlooking the river.

7 From this viewpoint turn sharp left, alongside wooden railings protecting the drop on the right. After 250yds (229m) the path forks: bear right, to pass through the earthwork to a small pond on the left. Turn left, with the ditch and earth wall of the hill fort on your left. After 200yds (183m) a Purple Trail waymarker points to the right. The trail, recently resurfaced in yellowish gravel, is unmistakable even without the waymarkers as it leads through the woods. It arrives at the tarred access track with speed bumps, close to the car park.