Travel: Between a rock and a hard place: In the first of an occasional series on undiscovered Britain, Magnus Mills searches for the Suck Stone, a gigantic rock somewhere in the Forest of Dean

MY DAD would never admit that he was lost. But he gave the game away when he climbed up on to a stump and began peering into the gloom. 'If it wasn't for all these trees we'd know where we were,' he announced.

'I know,' I replied, 'but this is a forest, so there are bound to be trees.'

Nevertheless, the trees were giving us problems. They were obscuring our quarry. We were not interested in trees today: we were looking for a giant rock. Somewhere in the Forest of Dean in Gloucestershire lies the Suck Stone, thought to be the largest detached block of rock in the British Isles. With an estimated weight of 14,000 tons, it sounded impressive. Britain's answer to Ayers Rock, albeit a modest one. The only trouble was that we couldn't find it. And we had been searching for hours.

The village of Staunton is surrounded by rocks with unusual names. Nearby is the Buck Stone, so called because it used to rock back and forth on its stony perch until a group of enthusiastic Victorians rolled it away one day, since when it has never been the same. Above the treetops is the Near Hearkening Rock, from where you can look across to Monmouth. And a mile away to the north is the Far Hearkening Rock. But the Suck Stone is the big one.

The plan had been to walk down the forest trail from Staunton to seek this huge rock, and report to the Independent that it was indeed there. Then we would continue down to the banks of the River Wye, have a can of beer . . . and then come back. It sounded simple. So simple that I totally ignored the advice in the Ward Lock Red Guide to the Wye Valley: 'Owing to the existence of numerous woodland paths, the unguided visitor may experience a little difficulty in finding the stone.' After all, I had an Ordnance Survey map. Furthermore, my dad was coming along, and he never gets lost.

So we had set off along the most likely looking trail and assumed we would come to the rock in no time. But those robust Forestry Commission tracks bear little resemblance to the neat little paths and byways indicated in the Ordnance Survey map. And the yellow waymark arrows are few and far between these days.

Combined with this was my dad's obstinacy: as we stood examining the map, a group of hikers came up the forest trail. 'Why don't we ask these people if they've seen a giant rock?' I suggested. But that was too easy. 'You don't ask people,' he told me curtly. So they went past, and all we said was 'good afternoon', then we were left in the forest surrounded by all those trees. After that I just followed him as we plunged down one leafy track after another. Being optimistic types, we kept expecting to come upon the elusive rock.

When we got to the River Wye we realised that we must have missed it. Never mind: we would find it on our return. In the meantime we could enjoy the meandering river.

An old dismantled railway led through the forest, forming part of the Wye Valley Walk. Striking east along this section we eventually came to The Biblins beauty spot. Here, in a deep bend of the river, rich pastures ran alongside the swirling waters. The sun came out and we sat with our beers admiring the Forestry Commission footbridge.

It is the noisiest bridge I have ever encountered. Suspended over the muddy torrent between two wooden towers, it proved a great attraction to children. Hordes of them ran across the wire-mesh walkway so it rattled and shook with every step. Back and forth they ran. Back and forth. Rattle, rattle.

Time was passing as we brooded over the map. We had to make sure we found the Suck Stone on our way back. 'If this rock is as big as you say it is, we should be able to find it,' said my dad, introducing a note of doubt, as though the whole thing might be a figment of my imagination. Yet there it was on the map (Pathfinder 1087), right beside a forest trail, at grid reference SO542140 It had to be there.

And so we set off back along another promising trail, and the whole cycle began again.

How many tracks are there in the Forest of Dean? I don't know, but I must have walked most of them. I suppose if we had examined the map in minute detail and used a compass we would never have lost our way in the first place. Instead we just charged headlong through the greenery and hoped for the best.

This was getting ridiculous. It was four hours since I had suggested speaking to those hikers, and I was beginning to think that I might miss the last train back to London. We could hear a distant church bell ringing, but we had no idea where we were.

Then, as we were frantically cutting across from one trail to another, we found it.

There it was, gracefully reclining in a shaft of sunlight at the foot of a slope. At last] The Suck Stone] So this was what we had spent the day looking for. A 60ft slab of rock big enough to flatten a house. Not quite Ayers Rock, but who cares? I'm not Australian.

We stood on the Suck Stone and jumped up and down. Actually, it reminded me of a giant slice of cheese, but that was probably because I was getting peckish. I attempted to take a photograph, but how do you do justice to a large stone?

I looked at the map and wondered how we could have possibly failed to find it earlier. Now I know where it is I could take you straight there. I think.

According to the map, the Near Hearkening Rock was close by. My plan had been to test the echo of the Near Hearkening with the Far Hearkening Rock. But I had a train to catch. That would have to wait until next time.

(Photograph omitted)