Architecture: Spaces available

WHEN PRINCESS Anne opens the new science gallery in Bristol, called Explore, on June 14 she won't be able to visit the walk-in womb. Or take the voyage along the sperm trail as it fertilises an egg on a wrap-around screen. This isn't to spare the Princess any blushes, but quite simply, the building will be empty. It is "opening" without its contents and will remain empty until spring 2000.

Fortunately Chris Wilkinson, the architect responsible for converting a 1902 reinforced concrete train shed here, has provided some amusements. A gigantic bubble-gum dispenser in transparent plastic full of purple balls, for example. As the balls are filled with salts, they change colour as the room heats up, till they get white hot - which is their way of lowering the temperature. The system is called Eutonics.

"The building doubles as a sort of scientific exhibit in itself," project architect Stafford Critchlow explains. But Explore must wait until the old Bristol Exploratory museum closes its doors and moves its contents into this new location before they can open. In the early 1980s, Exploratory popularised science with hands-on exhibits. They applied for Lottery money to celebrate the Millennium, but were told they had to have a new building to get any money. So that's how Explore was born. Not with a big bang but more of a begging bowl.

"We said the Princess would be first through our doors and so she is," is how Gillian Thomas, chief executive of @t Bristol, tersely explains the opening that really isn't. @t Bristol is the catalyst for what will be a pounds 400m urban rejuvenation scheme across 66 acres of the river front with a mix of public and private spaces. They have peppered sales literature with words like "Imagin@tion" and "Cre@tion" as Bristol reinvents itself as a Landmark city with pounds 41.3m of lottery money.

But there are some holes in this mix of commercial and public development on the former wasteland of the harbourside. Like the car park that doubles as an exhibition centre deep underground. It seems strange to put art underground in a car park, but the organisers of @t Bristol need to attract users. Besides, they're unabashed about littering the place with art. The car park was built to serve the performing arts theatre that doesn't exist, after the new Arts Council chairman, Gerry Robinson, refused a bid for pounds 55m to fund it. Sophisticated ducting can whisk away exhaust fumes from 530 cars as they rev up after nightly performances. Now the car park is looking for a new role - and revenue.

While it will still serves as a car park in the daytime, it is being threatened by a property developer's proposals, currently up for planning permission to build another car park for 700 vehicles nearby, along with a casino, nightclub, gym and office blocks. Planning permission has not been granted yet, and the plans are up for referral after the Cathedral complained about it blocking their sight lines. Not only the clergy are concerned.

"We had enough difficulty persuading the Millennium Commission to fund a car park in the first place," says architect David Caird from the Concept Planning Group, who did the masterplan for 11 acres at the core of the 66-acre site. "And yes, I am worried and disappointed by the plans to develop the site in the hub of the public space."

Caird's beautifully landscaped plans still show the faceted glass cantilever of a theatre on the waterfront, by the German architect Beynisch. When you see it you realise what a hole in the ground its absence leaves. It shows tree-lined containers, benches and sculptures.There will be a black slate fountain by William Pye, which can be drained in one section to turn into a huge amphitheatre. The big, paved square that roofs the underground is dotted with helicopter lights. Computerised by artist David Ward to plot the sun's movements at its zenith throughout the year, it shows a great figure of eight moving about on the square.

Bristol's hopes for five million visitors to the harbourside are now pinned on two attractions: Explore, in a listed train shed converted by Chris Wilkinson; and WildScreen IMAX cinema and greenhouse by Michael Hopkins.

Wilkinson had to convert the 1902 listed building with its thin, vaulted columns without alienating English Heritage, at the same time as showing off cutting-edge scientific achievements in a building designed for steam trains. And Hopkins had the even more challenging task of recreating indoors a rainforest micro climate that could support 150 species of flora and fauna without misting, fogging, or drying out. At the same time Hopkins had to build a state-of-the-art audiovisual IMAX cinema, and incorporate it on a trapezoidal site with an existing listed leadworks.

It is clear from his conversion that Chris Wilkinson likes Hennebique's industrial shed. The ground floor is triumphal which is why Wilkinson left it that way, adding a northern gallery with double height glazing that will be bathed in coloured light. Membrane is a digitally operated light piece, by artist Tessa Elliott, that translates silhouettes of passers- by on to the glass with coloured light that moves as they do. Chris Wilkinson distances his new addition from the old with a fine line shadow gap, before changing the surface material and the flooring. Conversely, this gap has the effect of making the transition from old to new seamless. On the first floor, which has poor floor-to-ceiling heights, he removed a forest of Y-fronted beams and created a double height exhibition space in the core. Upstairs, openings are controlled for audiovisual display in what he calls the black box area - although he has cheered up even that dim lighting level with strong colours.

Just as Wilkinson's building open-facedly shows off its architectonic features, like his purple Eutonic heating system, Hopkins hides his technology in this natural world at WildScreen. Admitting that brickwork is still "primitive technology", Hopkins' project architect Andy Barnett says that the continuous circle of the double-skinned cylindrical tower for the IMAX wouldn't have been possible to plot without computers (although Brunel didn't have that difficulty from his bricklayers).

On plan Hopkin's building resembles a gigantic bumble bee with its big, bug-eyed head, the cylindrical IMAX cinema and transparent wings on either side. Rather than glass, these greenhouses are made from a transparent fabric called ETFA, in little pillows. Shade in the rainforest is as much of a problem as light, so they have a tensioned blind system. Then they had tussles over the microclimate to get the right conditions for plants growing in specially controlled conditions.

Double-skinned for hidden ducting and cabling, the brick cylindrical tower that houses the IMAX cinema is reached sequentially on a route through transparent greenhouses on either side of the entrance. Not surprisingly, WildScreen is running late, and over budget.

Bristol currently represents everything that is wrong about not having an overall national policy about lottery funding. They relied on the Arts Council promise of pounds 55m for an Arts Centre, which then fell through. Lottery money from the Millennium Commission (pounds 41.3m) needed matched funding for the projects to get off the ground which unleashed hungry developers on the site of the reclaimed harbour. But Gillian Thomas is single-minded in her pursuit of the urban regeneration she has generated. "It's been a very good public and private partnership," she insists.

If Bristol is to be a landmark city for the 21st century, the private sector needs to get on line with @Bristol. Casinos have no place on the waterfront development, anymore than another car park. These are 20th- century concepts.