But from Earth in Edinburgh, to the Eden Project in Cornwall, from the Deep marine complex in Kingston-upon-Hull to the Centre for Life in Newcastle, the Millennium projects are in trouble. Within a year of opening, all of them have scaled down their original architecturally exciting schemes. With lottery grants dependent on matching funds from commercial sponsors, the dreams often turn into mere pedestrian bricks and mortar.
Pity the poor organisers of the Earth Centre, outside Doncaster, who had to kick-start sustainable eco-chic ideas in a closed-down coal mine. They had to reject would-be sponsors who were not squeaky clean enough for the greens, as well as become the environmentally-friendly model for the construction and landscape industry. Even common-or-garden fly-spray in the organic gardens has been replaced by marigold, mint and basil borders.
The Earth Centre nestles in the old slag heap left by two closed coal mines, Cadeby and Denaby, outside Doncaster in south Yorkshire. It looks green enough, with 35 acres of expensive top-soil covering the heap, a forest woodland taking root and latticed domes as plant-climbing frames to make the featureless landscape more interesting.
There is an organic food restaurant, the Planet Earth visitor centre and a water purification plant for waste water, with aquatic plants growing in it. The 400-acre site measures up to the chief executive Jonathan Smale's definition of sustainability, which he explains as "finding a way to live on this planet, that enables human development but which doesn't irrevocably damage systems, so that the generations coming after us have the same basic rights."
Put that together with the Millennium Commission's tough remit to find 50/50 funding and maintain visitor levels without dumbing down, and you will see how hard the Earth Centre has battled to get off the drawing board.
And will it attract the projected 500,000 visitors in its first year? Green tourists arriving by train, bike or on foot will be rewarded with a 40 per cent discount on their pounds 4.59 entrance fee. But motorists will pay the full fee, and be whisked from the car park by the bike train - the first electrically assisted, pedal-powered rickshaw in Europe. On launch day this week, it had broken down.
The newly installed waterless loos weren't working either. "It's so powerful that it would suck you into the sewage system and blow you away," Mr Smales explained when he refused to let me visit this particular tourist attraction. The waterless lavatories are billed by Earth Centre spin doctors as second only to the "amazing rotating Planet Earth Galleries" and the solar-powered lamps.
Throw all the superlatives you like at the Earth Centre attractions - and they did, from "futuristic, surprising, magical and breathtaking in content" - and what visitors are left with is a water purification plant, designed by Will Alsop, which recycles water into ponds to sustain plant life, and a featureless wedge of a limestone building, tucked into the disused colliery, by Richard Feilden and Peter Clegg.
These are the amazing rotating Planet Earth Galleries .Inside two exhibition halls, two 20-minute shows are staged. If Stephen Hawking is to be believed, two kilograms of matter hurtling about in the void exploded in a flash of light with a bang big enough to form our little planet Earth, but the sound and light show played out on glass panels in the centre of Planet Earth sounds a trifle subdued. The Earth music is played up from the floor in solemn, E-flat pieces from Bach and Mahler, while the outer fringes have shrill, F-Flat sounds accompanying images of pollution. This is actually a crowd-control device to keep visitors moving into the middle, away from the fringes and on towards the shop.
Planet Earth will have a dark, subterranean feel - a bit like being underground in a coal mine - and the acoustics have a nine-second echo like that in a cathedral. The most remarkable feature of the down-to-earth building is a labyrinth floor which regulates the temperature of the building without energy loss by drawing in air through vents, warming - or cooling - it, then recirculating the air.
If the system works - and the Romans pioneered the idea - why does this Millennium landmark project open next Easter, only to close six months later for the winter?
In The Future Works newsletter, Jonathan Smales explains that the Earth Centre exists to help individuals make decisions, however small, that will make a significant and positive impact on the future. "Our role is to show that people can influence the world around them, and that global environmental problems like climate change and the loss of biological diversity are not abstract concepts but real issues that relate to their lives." So why don't they stay open in the winter and show us how to keep warm and dry without puncturing the ozone layer?
What the Earth Centre needed was a big, state-of-the-art green-house with climate controls. Ironic, really, because that is exactly how it started out, with a huge, glazed Ark spreading its butterfly wings of solar-powered cells over the slag heaps. The Ark, by Future Systems, was designed to use sunlight to create an indoor rainforest and replicate different climate zones. One of the first projects to apply successfully for lottery money (pounds 50m), the Earth Centre started off as a swan but ended as an ugly duckling.
So far the Millennium Commission have only given them pounds 20m, so now everyone talks about the 66-acre development as Phase One. Phase Two will be Alsop's lopsided, crinkly tower, 28 metres high with a silicone glass skin over steel. Set to open in April 2000, the tower will house the "new Millennium cities show" which raised pounds 4.5m from the EU regional development fund.
The Earth Centre is not so much recycled as reinvented. Acid rain couldn't have been more destructive to the Ark than the tinkering about with the original concept. Jonathan Smales still insists that the Ark will be built in Phase Three, but can't say when that will be. The "techno organic architecture" that was to be an ecological masterpiece, will instead house a convention centre servicing the business park office blocks and new hotels also planned.
The centre's new MD, Alastair Creamer from London's Chicken Shed theatre company for children, is full of optimism. "This is a must-see attraction," he said. "For me, it has become a `must work for' one."
Once, the two coal mines here employed 2,000 people, but since the last pit closure in 1983, seven out of 10 families have stayed out of work in what is one of the most deprived areas of Britain.
As Britain turns into a service industry, the unemployed will be trained as shop assistants, minders, greeters and waiters.
The Earth Centre is recruiting 120 men and women to train at its Academy. So when it opens, former coal miners and their families will be back down at the old pit, dressed up in Swampy-style fatigues to amuse the kids. Earthonauts, zooming about on mountain bikes, will monitor the crowds.
And the locals still ask Jonathan Smales: "What does the Earth Centre make?"