THERE is a funny cartoon on the wall of the exhibition room at Kelburn, part of a display describing the origins of the Ayrshire estate and its owners, the Boyles.

In a speech bubble above his head, a man announces: "I'm Boyle, I'm rich and significant." David Boyle, the current Viscount Kelburn, gives a loud, short laugh. "There was a time when that was true," he says, wryly.

Boyle will inherit Kelburn Castle and its 3,500-acre estate in Fairlie, near Largs, from his father, Liberal Democrat Peer Patrick Boyle, who is the 10th Earl of Glasgow. The 35-year-old architect and his sister Alice spent their childhood at Kelburn, which opened to the public in 1977.

It has survived a difficult few years - poor weather, a fiercely competitive local tourist market and a fire have all been challenges to overcome - but David is the driving force behind ambitious plans to turn the visitor attraction into a hospitality venue and holiday destination.

Boosted by a £2.4 million investment - funded by the sale of 18 acres of land for housing - Kelburn now has a new pavilion, fancy glamping facilities and a castle fit for weddings. There are long-term plans for log cabins, yurts and teepees and David is busy organising a packed summer of events, including a boutique music festival called The Garden Party and Kelburn's first-ever Games Festival, incorporating Europe's strongest man and woman competitions.

"It does feel like we are really going for it," nods David. "We are catching up, but there is still work to be done." There is a mix of enthusiasm and relief in his voice - as the man faced with reinventing Kelburn, the weight of responsibility to the business, to his family and to the generations before him, lies heavily on his shoulders.

"It is a blessing and a curse," he admits. "It's good to have a ready-made sense of purpose but at the same time you do find yourself wondering what you might have done had it not been for this."

He pauses. "My mum said to me, several years ago - remember, you do have a choice. But it scares me, a little, to even think that way." It's a subject he returns to later, over mugs of tea in the family kitchen, a fabulous room complete with Aga, messy bookshelves, freshly laundered sheets hanging from a pulley and a cheeky cat called Chicken.

"I always knew I would come back here, it was just a question of when," he explains. "But I always wanted to be an architect too. I loved designing and drawing from a young age. And I've kept my hand in, with several of my design projects coming to fruition now."

They include work on a new, modern extension to Fairlie Castle and a garden centre project. "Architecture is very exacting, I prefer the creative side," he muses. "Would I have become a career architect anyway? I'm not sure."

David was born in London but moved to Kelburn as a toddler. Most children, on being told they were moving into a castle, would be beside themselves with glee. He felt differently. "At first we lived down at the centre, in what is now the rangers' house," he recalls. "When we had to move up to the 'big house' I was distraught. It felt like I was moving miles away from the park and all the fun stuff we got to do there."

David was educated at Gordonstoun and then studied architecture at Newcastle University. After a spell with an Edinburgh interior design company he worked for a local developer, designing houses in Millport on the isle of Cumbrae.

"I came back to Kelburn almost by accident," he says. "The general manager was ill, the head ranger had left, so I came in to help out and worked here for 16 days in a row. And because my dad doesn't do email, and I do, everything - bank details, insurance, suppliers' information - all of it came to me. Suddenly, it was apparent it was time to take over."

One of his first initiatives was the Graffiti Project, a spectacular piece of psychedelic urban art that embraces the walls and turrets of the south side of the castle. As bold artistic statements go, this was up there with the best of them.

"My dad found it hard to swallow at first," grins David. "But he was very supportive. And the media coverage was unbelievable - in the end we had a global television audience of around 70 million."

Now, the mural has to go, as the cement coating on which it is painted is causing damage to the original castle walls. "It will be a shame but we plan to run a competition for artists and designers to come up with something to replace it," he says, his eyes lighting up.

"It could be anything - audiovisual elements, maybe, lighting behind the render, we just want to put it out there and see what ideas we get back."

Boyle is a whirlwind of energy and admits he finds it hard to switch off. Sometimes, he can escape to the Plaisance, a beautiful walled garden in the heart of the estate, with friends and a glass of wine. "When I was younger, I remember playing in the sunshine, guilt free, but now…" His voice trails off. "When I am here, I find it hard to relax. There is so much to do."

He pauses. "But although I'm too stressed to enjoy it, I always appreciate it. It's magical and I love sharing it with people."

His enthusiasm for Kelburn, and willingness to muck in, has endeared him to the staff. On a whistlestop tour of the castle and grounds - "do you have to walk so fast?" his PR consultant complains as he stops to pick up bits of litter.

"I'm sorry, I can't help it," he apologises, slowing to a sprint. "It comes from diving about from place to place on the estate, particularly during the music festival." He swoops down on an unsuspecting sweetie wrapper. "I can't walk past it, sorry."

For all his, aristocratic eligibility, Viscount Kelburn is "just David", one of the team, who is determined to make a good go of it.

"I don't really use the title," he shrugs. He shies away from publicity - this is his first interview since a bad experience with a television company.

"They claimed to be making a genuine documentary about Scotland's aristocracy and the problems of succession and so on, but when I saw the first draft of it, I was speechless," he says, his eyes darkening at the memory. "They made it look like we did nothing, just sat around all day. It was awful."

He adds, with mild frustration: "I know it is unpopular and unfashionable to be a member of the aristocracy and some people like to put the boot in.

"But there is a lot of misunderstanding. People think we have wads of cash and hold champagne breakfasts all the time. In fact, some of us are working hard to keep things in order, at a cost which would otherwise be borne by the taxpayer."

He relaxes. "I hope people do see what Kelburn is to the local community, and to Scotland," he says. "We have a good atmosphere here, people work hard and there is a lot to do, but at last, I think, things are turning around."