Architecture: Did the earth move for you?

Architects' sensitivity about their buildings once the clients move in is sometimes seen as arrogance. "Clients must have somewhere to be seated, eat and sleep - damn them," Frank Lloyd Wright once observed, long before the electronic age introduced its own demands on modern architecture.

Now that most information is received on screen , we need more darkness with which to read them. Yet modern architects, dedicated to light and space, beam in as much light as possible. This predilection puts them on a collision course with exhibition curators, called "imagineers". Interactive display needs more darkness. Transparency is as undesirable for sound and light shows as metallic surfaces. Visitors clog up space with viewing platforms designed like bits of spaceships or cockpits of planes or the bridge on a submarine. Screens at kiddie- height play havoc with space and proportion. The gallery as a white box is an outdated concept to wireheads. They'd just as easily stage a sensational show in a coffin.

"Galleries today are modern-day cinemas," architect Michael Hopkins observes. Unlike the Victorian architects who spent all their energy beaming daylight on to exhibits, when he was asked in 1988 to house the Dynamic Earth tourist attraction and theme park inside a new convention centre called William Younger Centre in Edinburgh, he buried a black box beneath the carapace of a huge tented roof and let the imagineers get on with it. Then he did what he does best, create a brilliant new public space that makes the experience of it every bit as thrilling as the white-knuckle rides taking place at its core.

Stepping on to the rooftop terrace at the William Younger Centre is like seeing the light, a big, calm, Zen-like white space underneath the ribs of the translucent bleached white roof coated with Teflon, same as non- stick saucepans. They call this space, which is big enough to hold a banquet for 1,000 people, the Stratosphere. Glass walls give breathtaking views of historic Edinburgh with the new Scottish Parliament beginning to cut ground at its feet, the Palace of Holyroodhouse to the east and the Royal Mile ending at Edinburgh Castle to the west. This roof space is free, and houses a cafe and restaurant with ticket booths for the pounds 4.50 admission to the Dynamic Earth centre below.

"You can take the dog up there for a walk," says Hopkins. "I think it will be popular." Undoubtedly, it will. With its spectacular views and sheltering skies, the building is as good a tourist attraction as the theme park within.

Hopkins's brief was to create a building that would put Edinburgh on the map in the same way as the Sydney Opera House came to symbolise Australia. In the next century, his building may well be eclipsed by the new parliament building designed by the Catalan architect Miralles - we shall have to see when it is built - but it was certainly the catalyst for the entire development of the Holyrood site. Without the Dynamic Earth centre, the Scottish Parliament would never have landed there.

Eleven years ago, construction work began on the pounds 15m centre to house the Dynamic Earth attraction by Event, and to pull some of the million visitors a year to Edinburgh Castle. Scottish & Newcastle breweries donated the site of the former brewery to the people of Edinburgh on condition that "a significant new building would be created to benefit the community", and pounds 3.5m was spent clearing up the industrial pollution from British Gas who also donated a bit of land. An early application for lottery money from the Millennium Commission raised pounds 15m because it was designated one of the Landmark buildings to celebrate the millennium. Its jaunty roof does precisely that.

"Sort of Jekyll and Hyde," says Pete Santer, from the Lothian and Edinburgh Enterprise Ltd responsible for regenerating the site. "Historic Edinburgh meets saucy modernity."

Michael Hopkins is very good at the sort of sleight of hand that modernising sensitive historic sites requires. At the much-loved Glyndebourne opera house he added a circular tower that gives performers as much space within the circle as the audience, a nice egalitarian touch for modern opera. At Lord's hallowed cricket ground he set a medieval tented roof atop the Mount Stand. His unabashed celebration of light and space induced him, with his wife Patti, who is also an architect and shares his practice, to raise his own family in an entirely transparent glass box he built in Hampstead.

So having buried the black box of Dynamic Earth deep in its core, he let the William Younger Centre grow beneath the carapace of its tented roof, resembling a giant pterodactyl wing spanning 16,000 square metres on site. "We'll never have a better site," he observes.

Dynamic Earth appears to have landed so lightly that the question most asked was "Will it blow away?"

Move around to the stony Salisbury Crags behind and you see that in fact, the William Younger building is anchored in a castellated, turreted stone wall left over from the Victorian brewery. Michael Hopkins climbed the Salisbury crags to look down upon those remains and decided to let them become the springboard for his flight of fancy with the roof. Even Edinburgh's stormy weather can't shift it, though Dynamic Earth has some spectacular film footage of the dismissive way in which Nature trashes architecture. Skyscrapers topple into the San Andreas Fault. Concrete blocks drown in tidal waves, they sway under earth tremors and they end up like Pompeii in the slipstream of molten lava. All on screen of course, but so realistically that I guarantee you'll take a breather in the Stratosphere above at the end of the visit, timed at 90 minutes.

Inside Dynamic Earth, the earth moves every five minutes. Take the volcano room where birdsong is stilled by a far-off boom. Smoke and a sulphuric smell fill the viewing chamber as red molten lava appears to flow from the walls. The floor shakes. It rumbles. The Big Bang begins as an explosion of stars glimpsed through windows of a fake Starship Enterprise. Instead of Stephen Hawking's voice-over you get Scottish actor John Hannah directly and simply explaining what is going on.

To learn about oceans you stand on a yellow submarine deck while sharks and fish circle the porthole windows. They're all on film but instead of square screens, curving them and setting them in this iron replica of Captain Nemo's sub helps the illusion of being underwater. So does the sound of escaping bubbles and deep breathing as though from a diver's oxygen apparatus. The rainforest is fibreglass sprayed green. Skyscraper trees reveal the inhabitants, floor by floor, from termites in the basement to squawking parrots in the penthouse.

Only one blip on the horizon is that the building, due to open this spring, will in fact open at the end of July in time for the Edinburgh Festival. The British Tourist Authority was so sure of the spring date that they have marketed it around the world in their "2000 Years around Britain" brochure. The organisers of Dynamic Earth have had to cancel bookings for banquets and conventions in the Stratosphere. Everyone pins the blame on something as mundane as design flaws in the kitchens, which were never envisaged to be used for banquets at the beginning of the project, but Michael Hopkins is quite sanguine about the fact that it was a question of money. "All millennium projects are tight for money," he says, and he should know because apart from the William Younger Centre he has designed Norfolk's Millennium Library and Wild Screen in Bristol, both Millennium projects.

Certainly, the original brief did change once Holyrood was chosen as the site for the Scottish Parliament. Dynamic Earth Trust has been quick to see the potential for money-making ventures, from renting out the Stratosphere as a convention centre and banqueting hall, to turning the amphitheatre in front of the William Younger building into a performing arts venue. Out went the garden planned with parterres and ha-has, and in came the coach-drop in the hub of the site. When it opens, Dynamic Earth is going to be the hottest spot in Edinburgh.