THEY CALL it the Well Of The Dead. A gloomy pit where the ghosts of a battle fought more than 250 years ago linger in the shadows. From the ground rises a lichenous, corpse-like rock bearing the inscription: "Here the chief of the MacGillivrays fell." These words, barely legible in the afternoon's winter light, unleash a shiver in the direction of my spine. The icy wind blowing across Culloden moor and down into this chilling war grave, just as it did when the men charged and the cannons flared on April 16, 1746, ensures it hits the target.

As I head up to the towering memorial cairn in the centre of the battlefield, a man marches past me like a soldier on patrol. His only weapon seems to be a raincoat, so I shoot a question at him. Why trudge across a depressing, desolate bog on a miserable day like this? Surely nearby Inverness, with its new metropolitan cafés and bars, is more inviting. The answer instantly reminds me why I, too, am here. "It's the history. You can feel it," he says in a cheerful English accent. "Whenever I'm up I always try to come. My wife thinks I'm mad." And is he? "I'm related," he explains with a solemn nod towards the acres of dead warriors behind him. With that, he continues his pilgrim's progress. But not before adding: "I think it's fantastic what they've done here."

The man, in whose footsteps many thousands of other people will follow, excitedly squelches off in the direction of the National Trust for Scotland's gleaming new £9.4 million Culloden visitors' centre. It is a low-slung, modern structure of local wood and stone, discretely camped on the edge of the field. The doors were tentatively unlocked just before Christmas for a "soft opening" designed to allow time for the smoothing out of any rough edges before a major official launch later this year on the battle's anniversary. It also allowed for the centre, due to have been finished much earlier in 2007, to be declared "open" before the so-called Highland Year of Culture was over. Now it is finally ready for action, the new building cannot fail to pull in the crowds. In fact, success would be guaranteed even if the place were but little improvement on the inadequate and deservedly doomed 1970s centre it replaces. Culloden, the place and the event, remains compelling.

The last major military engagement to take place in mainland Britain, the battle and its aftermath witnessed the plucky, sword-bearing Scottish clansmen of "Bonnie" Prince Charlie's Jacobite army being liquidated by the bloodthirsty, musket-wielding English redcoats of "Butcher" Cumberland's Hanoverian war machine. It was an epic showdown to the 1745 Rebellion in which a rag-tag band of rustic, mediaeval Highlanders were clinically mowed down by a modern, sophisticated Lowland opposition, leaving the surviving clansmen to be cleared off their homelands and forced to emigrate for survival. Traditional Highland society thereby collapsed and with it the last bastion of resistance to Scotland's incipient Union with England.

Or, at least, that's the legend. Academic historians know the full picture of Culloden is not nearly so black and white, and they spend a lot of time debating exactly how many shades of grey were involved. But that's not very exciting. So Culloden lives on in the popular imagination as one of history's great tragedies, with northern Celtic heroes on one side and southern Teutonic villains on the other.

Educating the visiting public about what really happened, without losing the magic, is one of the new centre's main aims. Earlier last year I went behind the scenes to witness the creation of the shiny, multimedia extravaganza inside. "You can press buttons on this panel here," explained one of the technicians, "and it will illuminate part of the battle scene on the wall over there." At the time the panel in question was still a mass of wires and circuits with no fascia and the screen was blank, but as with setting up toy soldiers the fun was in imagining what drama would unfold once everything was in place.

Now the centre is complete, it offers a much enhanced experience over what went before. The building itself, designed by Glasgow-based Gareth Hoskins Architects, expertly shields the battlefield from view when you arrive in the car park. This had the effect of lighting a fuse of anticipation about what was hidden on the other side - even though I had visited the field before. I felt myself drawn through the entrance and into the multimedia exhibition, loaded with stories from the battle, before heading up on to the roof to be flanked by the turrets of the eco-friendly ventilation system. Finally, I looked out on a commanding view of the moor and the fuse of anticipation exploded.

My thoughts rained down like cannonballs. I pictured a moment, amid the smoke and clanging of claymore against bayonet, when the Jacobite chief Cameron of Lochiel apparently had to be carried from the field after both his ankles were shattered by grapeshot. Or when the prince, realising all was lost, fled the scene with its four-deep piles of bodies and one of his own men, Lord Elcho, reportedly shouted after him: "Run, you cowardly Italian!"

For this visitor, at least, the new Culloden battlefield experience is a victory. Despite all its iconic importance, however, the flagship development is only part of a much larger battle being waged by the organisation that owns the site. The trust is facing a funding crisis. It has £170 million net assets but most are restricted for use on specific properties or activities and cannot be diverted to areas desperately short of funds. Visitor numbers are in decline, as is cash from legacies. The number of membership subscriptions, the trust's largest income source, is growing but at far too slow a rate to meet the rising costs of owning, maintaining and staffing its nationwide portfolio of battlefields, castles, gardens, houses, munros and islands. Projects like Culloden, or the new pier on the island of Canna, are only possible with large grants from the state or other external sources.

So how did this precarious situation arise? And how can headline projects such as Culloden generate enough sustained interest to save the trust and the properties in its care from ruin? The search for answers takes me 150 miles south to the New Town of Edinburgh where almost every street is named after the Jacobites' victorious enemies. The address of the trust's headquarters, Charlotte Square, honours the queen of the Hanoverian George III, whose descendant Prince Charles, Duke of Rothesay, is the trust's patron.

When I arrive, I find a woman is holding court. Shonaig Macpherson is the first female chairman in the trust's history (she rejects the gender-neutral "chairperson"). "The decline in the number of people visiting our properties is obviously worrying," she tells me. So why is this happening? "One reason is increased competition. From other heritage organisations, other charities and other forms of entertainment. We all compete for members, supporters, visitors and tourists. It's tough."

Another reason, it becomes apparent, is that the trust has shot itself in the foot. Set up in 1931 to conserve land and buildings of natural and cultural importance, the NTS has suffered in recent times from a combination of amateurishness, elitism and complacency in its ranks. This has allowed it to drift dangerously out of touch with the visiting public upon whom it depends for survival. Macpherson's chairmanship, which began in 2005, appears to have ushered in a period of clarity, if not an instant reversal of fortune. Since news of the trust's financial troubles first emerged in 2006, its short-term position has worsened, with a £1.6m decline in the trust's working capital. But turning around an organisation like this after decades of poor management is not unlike steering an oil tanker. It takes time. Macpherson, crucially, has recognised that muddling along is not an option, and a top-down effort does appear to be gathering momentum to create a businesslike heritage body fit for purpose in the 21st century.

"That's why Mark is on board," says Macpherson, gesturing towards the man sitting next to her. Mark Adderley has been chief executive for less than a year, one of several key appointments made during the past 12 months. So what's his plan? "At the moment there are still some of our properties where young children might turn up and be met by a frown rather than a smile," he admits. "That has to change, and we are changing it by working with our staff. We want families to feel welcome and we want more families to become members." This recognises the cold commercial fact that a new crop of members to replace the elderly ones who pass away has to come from somewhere, hence the new Culloden centre has a very child-friendly atmosphere.

Adderley is also in the early stages of implementing a three-year plan to save £3m on operating costs. That means removing layers of bureaucracy. And that means cutting jobs. This is guaranteed to stir up some bitterness and resentment in the short term, but the long-term goal is seen as too important for such tough decisions to be ignored. A more palatable challenge, meanwhile, is finding ways to communicate better with members and the wider public without breaking the bank.

The trust's last TV advertising campaign, which tried but largely failed to appeal to young people, was by all accounts an expensive disaster. The emphasis is now on an improved website and email bulletins, and spreading word about the trust on local radio and in local newspapers. "People often don't know we are a charity which has to pay for itself," says Adderley. "And many still don't realise we are a separate organisation from the National Trust in England. That's a very common problem we have."

Macpherson and Adderley know that to reach a greater number of people they must do more than tightening their belts or breathing new life into old favourites like Culloden, the island of Canna or the Robert Burns Birthplace Museum. What they really need is to promote a new vision, indicated by the organisation's new slogan: "A place for everyone." This means the trust isn't just for history and heritage buffs, especially when it comes to its gardens, parks and nature reserves. It is also a place for environmentalists, sporting enthusiasts, leisure seekers and socially excluded groups. "We work with other organisations such as the Prince's Trust so that people who wouldn't normally think about visiting our properties get the chance to do so," says Adderley.

The core of what the trust is about, however, remains conserving the nation's heritage. But it is in this area that there is arguably room for further radical and popular thinking. A couple of weeks before our meeting I watched Macpherson address an academic audience at Edinburgh University's Playfair Library. When it came to the question of the trust's relationship with the public and how it could be strengthened, she hit upon a problem.

Why, Macpherson wondered, are people fascinated with such structures as the Forth Road Bridge while precious buildings in the trust's care - meaning certain stately homes - struggle to attract visitors? In other words, why care about a unique 1960s suspension bridge facing an uncertain future when there is another rich laird's mansion requiring our attention? The deeper problem, it seemed to me, was Macpherson's struggle with the idea of 20th-century architecture having any great merit. Yet many of the people she wants to connect with clearly feel that it does.

When we meet I put it to both Macpherson and Adderley that the built heritage of the past century, an era defined by several steel and concrete structures that arguably deserve conservation, is virtually ignored by the trust. They offer no protest. There is a strange irony here, in that the new Culloden centre may yet go down in history as a well-regarded example of early 21st-century architecture. But what about the 1950s and 1960s? Basil Spence? Gillespie, Kidd and Coia?

Macpherson's face lights up at the mention of the latter firm's derelict St Peter's Seminary at Cardross - a breathtaking modernist structure that could be up for grabs. "It definitely has value," she says, before adding with a furrowed brow: "But what would we use it for?" Given the building is on the World Monument Fund's list of the 100 most endangered sites in 2008, perhaps it's time the trust canvassed the much-needed, potential new members for suggestions.