FORGE Valley near Scarborough has quite a heavy name, hammering out a reminder of medieval charcoal making and iron working. Ten millennia before that, the valley was gouged out violently by meltwater. It's still deep, steep and narrow, and "oversized" for its river.

The English Nature info boards attest to the rich and rare wildlife in this National Nature Reserve, but their maps are stingy on walk route information. So we asked a bird benefactor at the Bird Watchers' car park where the nearest bridge was. He directed us to the small but perfectly hygienic Old Man's Mouth car park, where the wavy tongue ferns glistened, pendulous sedges provide an all-year green beard and a fuzz of mosses coat cosy insect hideaways and shelter boils of scarlet fungi.

The wooden footbridge is over the River Derwent, here a steady clear uniform flow a few yards wide, a foot or so deep. Beside it run duckboards, slithery, though in the process of non-slip resurfacing. Boardwalk for a duckwalk, if not Chuck Berry style, then a slow waddle past the riches for half a mile.

The otters are rarely seen but one's advised to look out for their spraints (droppings)' or listen for the distinctive plop'. There was a feel of life, the ground did not show the hammer of the winter.

The duckboards stop and the valley changes shape, widening, acquiring a slopping terrace of pasture. Three herons lifted from the grass and exercised their five or six foot wingspans on a sweep of the misty air to land and watch, grey sentinels in the tops of the highest skyline conifers. The Derwent and environs hold heron food, including brown trout, grayling and crayfish.

Our route kept touching on the little river that now it's out of the trees has reeds and space to meander. A dipper caught the eye on a mid-stream rock. We walked by dry grooves in the pasture that are the shapes of previous flows, some straight some horseshoe curved, most with alder trees, a crescent held winter water. The convoluted line of the Derwent here is virtually the same as on an 1854 map from www.oldmaps.co.uk After a couple of miles, it was time to turn around and climb the valleyside by way of a sunken path, quite a deepened gully, and then a track at the tree line. Here we stopped for a sandwich, the mist, well rain, blurred the view towards Hackness. Half a dozen long-tailed tits came close and flitted around us in a hazel tree, and they weren't after the catkins.

Yes, tracks now at higher altitudes, better draining limestone and grit underneath a layer of autumn sown crops. Three deer saw us from half a mile away, watched intently and then bobbed into the woods as we closed.

That just left the way down the very steep side of Forge Valley. Luckily there is a most efficient and comfortable zigzag descent that is on the 1854 map.

Directions

When in doubt look at the map. Check your position at each point. Keep straight on unless otherwise directed.

1. From Old Man's Mouth car park, footbridge over River Derwent and right to duckboard path.

2. On right-hand bend about 100 yards before field and end of duckboards, fork left up steps/slope with handrail, 100 yards, stile into field. Path angles gently down with old hedgerow/gorse to right. Stile/fieldgate above gorse, down to stile/fieldgate by river.

3. Left before gateway. Pass pool of water to your left, 50 yards, gates/stile and left (waymark), stile/fieldgate (waymark), cross field, footbridge and stile in holly hedge 20 yards from river (waymark).

4. Fieldgate/cattlegrid to hamlet, 20 yards, fieldgate on left (no sign) to track up by trees, fieldgate, fieldgate into wood.

5. At top of hill left to track for 20 yards, fieldgate on right (no sign), 11 o'clock across field towards gate but turn left immediately before it and cross field to fieldgate to track.

6. Join road for 50 yards, left to Spikers Hill Farm, through yard, right to path at edge of wooded slope (fingerpost).

7. Left to good wide path downhill (no sign). On bend below Spikers Hill Farm ignore faint path straight on and take path that swings right downhill with steps (no sign). Right to duckboards to rejoin outward route.

Fact file

Distance: Five miles.

Time: Three hours.

General location: Near Scarborough.

Start: Old Man's Mouth car park, signed and free.

Right of way: Public and open access.

Map: Drawn from OS Explorer OL27 North York Moors eastern area.

Date walked: February, 2007.

Road route: Forge Valley signed from East Ayton.

Car parking: There are other car parks nearby.

Lavatories: None.

Refreshments: East and West Ayton.

Tourist and public transport information: Scarborough TIC 01723 373333.

Terrain: Valley.

Points of interest: Petrifying springs.

Difficulty: Moderate.

Please observe the Country Code and park sensibly. While every effort is made to provide accurate information, walkers set out at their own risk.

Map of the walk>>