Gardening: At the altar of a better class of madman: If you think Alton Towers is crazy now, you should have seen it 170 years ago. Anna Pavord visits its wonderful gardens

IT WAS not the Double Corkscrew, nor the Thunder Looper, nor even the Waveswinger that caught my fancy when I went to Alton Towers theme park in Staffordshire. It was the thought of the blind harpist hired by the 15th Earl of Shrewsbury to play while he strolled through his gardens at Alton in the 1820s.

The earl was clearly a madman of the very best sort. He transformed a Georgian farmhouse on the site into a Gothic castle of Disney-like proportions. There was a vast conservatory, a chapel, towers in abundance, crenellated battlements - but, according to one account, 'scarcely a habitable room'.

The house stood on a flat plateau overlooking a wooded valley. This valley became the earl's private Elysium. He marked out the boundaries with huge scalloped walls of pink sandstone. He terraced the slopes of the valley and decorated the retaining walls with row upon row of urns and statues.

Robert Abraham, the ironmaster, designed a Gothic watchtower, raised on a fake bluff of rock beyond the house. Abraham was also responsible for the delicate three-storey pagoda set in the middle of one of the lower lakes. A jet of water, 100 feet high, spouts from the top of the pagoda and falls in a soft sheet over the bells hung around the curled roofs.

This would be more than enough for most garden-makers, but the 15th earl had scarcely got the bit between his teeth. John Claudius Loudon, the garden designer and prolific author, visited Alton Towers in 1826, the year before the earl's death and found 'trellis-work arbours, vases, statues, stairs, pavements, gravel and grass walks, ornamental buildings, bridges, porticoes, temples, gates, iron railings, parterres, jets, ponds, streams, seats, caves, flower baskets, waterfalls, rocks, cottages, trees, shrubs, beds of flowers, ivied walls, rock-work, shell-work, root-work, moss houses'.

And, of course, there was the harpist, who had his own house, built by the earl on the gloomy side of the valley. How did the harpist know when to play, I wonder? Did someone let him know when the earl was on his way to the garden, or was he contracted willy-nilly to give a burst of 'Dafydd and the White Rock' every evening at 6pm in the hope that his employer was taking a preprandial stroll? Anyway, the harpist's house is the Swiss Restaurant now and Henry Hound's Super Sounds have taken over the job of providing music.

There is a curious fitness in Alton Towers being a theme park. It was a fantasy world from the beginning. The Haunted House, a new attraction this year, is merely a more sophisticated version of the spooky grotto built in the 19th century under the watchtower. The grotto is shaded by a yew tree and the entrance is guarded by huge slabs of fake rock. I'll bet the earl had a hermit there, to lurch out and frighten guests at dusk.

Though the finer touches have gone, there are still enough of the garden's extraordinary features left to make visitors realise what a stunner it must have been in its heyday. The pundits were suspicious of it even then, because it did not conform to any rules. 'This nobleman,' wrote Loudon, 'abounding in wealth, always fond of architecture and gardening, but with much more fancy than sound judgement seems to have wished to produce something different from everything else . . . ' Loudon evidently thought this a dangerously odd thing to do.

The earl did not lack for advisers, Loudon among them. But after consulting them all, he rejected their advice and followed his fancy, which evidently annoyed them. But what professional would have suggested the dotty fake Stonehenge that looms up above one of the ruined conservatories? Or the bizarre corkscrew fountain, like a four-tier wedding cake, that sits below the watchtower?

There is no way into the garden except through the theme park, which is a pity. By the time you have queued to park, queued for the monorail ride to take you from the car park to the centre, queued for your ticket and queued to get the ticket stamped, you begin to wonder if the garden is worth the effort. It is.

Once in, you can head straight towards the big lake with the rowing boats. The garden lies in a bowl below that. The house is a shell, but it is worth walking up to just to see the patterns the light makes as it splinters through the vast stained-glass windows of the banqueting hall.

A path leads down under the causeway that dams up the lake and takes you past a white, cast-iron monument to the earl. There is a superb Japanese maple next to it and a good view back over banks of evergreen towards the house.

The planting that remains is mostly the work of the 16th earl. There are excellent pines, good rhododendrons, splendid maples, surprising magnolias, and their bulk softens what must once have been an overpowering amount of architectural masonry.

The garden is largely contained in a natural bowl, with water at all levels. The water is not natural. The earl piped it in from a spring two miles away to make his lakes and jets, formal pools and fountains. Bringing it to the house seemed a secondary consideration.

The path leading along the top level brings you to Abraham's conservatories. They are astonishingly elegant constructions, seven domes with ribs of iron and small overlapping panes of glass as neat as fish scales. The biggest dome is topped with a gilded coronet. The rest have pineapples.

The front of the range is classical, only the barest wisps of stone holding together a confection that looks as fragile as spun sugar. The conservatories are under-planted and the great central basin is empty, but be satisfied with the miracle of the building having survived at all.

Steps lead down from the conservatory terrace by the belvedere to a lower walk through clipped hoops of yew. A herbaceous border runs underneath the wall and ahead is the extraordinary watchtower, perched on its rock. A new cable railway now drops passengers there.

At the end of this terrace you can peer over scrolls of stone on to a water staircase that drops from the top lake down to the string of lakes at the bottom of the valley, where the pagoda fountain is situated.

Early photographs show that the pagoda was once reached by a bridge, which is no longer there. Meadowsweet and huge clumps of the royal fern, Osmunda regalis, grow by the water's edge. As you walk back through the foot of the valley towards the house, perched on its high plateau, you will be facing the rock garden that fills the bowl directly under the earl's monument.

To get to it, you must cross a low iron bridge slung across a canal and then climb up through banks of heather and yucca and broom and evergreens clipped into drunken cones and pyramids. The path takes you across a pool with square stepping stones.

As soon as the 15th earl died, his successor began to simplify the garden, but still the pundits were not satisfied. 'No trifling alteration can ever improve what is so far out of the reach of reason,' thundered one. Loudon agreed.

There is no sign now of the huge serpent that Loudon talks of with iron tongue and glass eyes, carved from a projecting rock. Nor of the Indian temple covered in hieroglyphics. Nor of the fake cottage which the earl made by sticking dormer windows on to a solid mass of rock, with heather for a roof.

But on the other hand, you have got the New Beast rollercoaster, Katanga Canyon and the Gravitron. Children, at least, on a bank holiday outing will think that is more than a fair swap.

Alton Towers is open daily until 8 November. Rides start at 10am and finish at 5pm, 6pm or 7pm, depending on the time of year. Admission for a full day pounds 12, half-day pounds 6. From 9 November to mid-March the garden and grounds are open to the public for a small charge. For further details phone 0538 702200. There is also a very good garden hiding in the fun-fair at Bicton Park, East Budleigh, Budleigh Salterton, Devon (0395 68465). Open March-October daily 10am-6pm. Entrance pounds 3.75.

(Photograph omitted)