An innocuous garden with high hedges, clipped lawns and well-kept borders give the visitor no clue as to what lies within. To the casual observer, the Tupgill Park Estate is like many in the Yorkshire Dales, hilly, green and cared for, sitting happily within the natural beauty of Coverdale.

But there is a hint in the name that, in this part of the Yorkshire Dales, there is more here than meets the eye.

The Forbidden Corner is a labyrinth of tunnels, chambers, follies and surprises created in a four-acre garden, one-third of which is underground, on the estate. Enter and you will discover the temple of the underworld, extraordinary statues, a huge pyramid made of translucent glass and paths and passages that lead nowhere.

The attraction has been a labour of love for owner Colin Armstrong but one that has won him wide acclaim. The Folly Fellowship hailed The Forbidden Corner the Best European Folly of the 20th Century. It was also recently voted the best children’s attraction in Yorkshire. Not bad for something that started out in 1979 as a windbreak and that developed as a bit of a lark for the kids.

“The place really does reflect my personality,” says Mr Armstrong, who runs an agro-chemical business in Ecuador. “I love the place. I go round it at least once a day when I am here. And when I’m in Ecuador I go through it several times a day in my mind. When business is going badly, you need something to dream about.”

An extension to the existing underground grotto has taken nine months to build at a cost of pound;150,000. Cat and Mouse takes visitors on a magical tour of a mouse hole and uses sophisticated animatronics, electronic sensors and hydraulics.

The journey follows narrow tunnels leading from one mouse scene to another.

In a mouse schoolroom young mice are warned of the dangers of the cat and instructed to “run, run, run” should they come across one. In a pub setting, old mice chat in thick Yorkshire accents about their near-death experiences with “Henry the mice mincer”. Beer is one grain per pint, according to the price list, while the pub menu includes cats’ tail soup.

“We had a real giggle planning it,” says Mr Armstrong. “We wondered if we should use live rats, then thought perhaps not.”

Also new this year is St Cuthbert’s Chapel, a derelict-looking folly that houses a “magic pool”. A “silver” swan, made from pewter and stainless steel, rests there for eternity having being lured to its fate by the magic waters. Entering the folly, a mechanical raven suddenly springs to life to warn visitors of the dangers ahead.

Last season saw 76 school trips totalling almost 4,000 children from all over the country. Indeed, The Forbidden Corner has become a vital element of the 800-acre estate, owned by the Armstrong family for generations. Mr Armstrong was the first to drop the reins of the traditional family business, racehorse training.

“We get a lot of school parties and we are included in an educational pack prepared by the local education authority,” he says. “A lot of school kids come from the towns and cities as a treat.

“It stimulates their imagination and the funny thing is that they see things that aren’t there. I heard one talking about the devil’s head in the main chamber and how it turns and watches you. Well it doesn’t, it’s in their minds. Other times they say they love more banal things like the stepping stones.”

Visits are often followed-up with classroom-based projects on what the children have encountered during their trip.

The Forbidden Corner is a magical world that appeals to visitors of all ages and, with the current obsession with Harry Potter and the Lord of the Rings, one that has become more popular than ever.

As the man behind it says, what visitors find there is limited only by their imaginations.

* Admission: Adults pound;5.50, Children pound;3.50. Season tickets and group rates are available for private party bookings and educational groups.Opening times: open every day from March 28 to October 31, and on Sundays until Christmas. Monday-Saturday noon-6pm (or dusk if earlier); Sundays and Bank Holidays 10am-6pm.Planning restrictions mean the park is limited to 120 people an hour so visitors must book ahead. Forbidden Corner, The Tupgill Partk Estate, Coverdale, Leyburn, North Yorkshire DL8 4TJ. Tel: 01969 640638; fax: 01969 640687.