The Glasgow Science Centre, or GSC, sits in the old docklands down by the Clyde in Govan. The streets of tenement housing and factories behind, stretching to the Ibrox stadium, are where Rab's outdoor scenes are shot. Further downriver, tall cranes mark the shipyard where Billy Connolly once worked as a welder. If you know Bilbao, you'll know that all this - Scottish comedians and Basque separatist movements apart - is remarkably similar to the run-down riverside district in Bilbao where Gehry built his Guggenheim and sheathed it in shimmering titanium. The GSC, too apart from the tower, is titanium-clad - the first such building in Britain.

It does not open fully to the public until May, but the buildings are almost complete and the exhibition fit-out is about to commence. This is Scotland's biggest single Millennium project, on the same scale as the mega-conservatories of the better-known Eden Project down in Cornwall, which has been built simultaneously and will open around the same time. Unlike Eden, the GSC has a more complex history, with more people involved. For a start, there are two sets of architects: Allen's firm BDP, or Building Design Partnership, working out of Glasgow: and the London-based architect Richard Horden, who designed the unique slender, rotating observation tower that is part of the complex - but which was built, confusingly, by BDP after Horden withdrew in protest at what he saw as dilution of his original concept.

What you see today are three linked buildings: Horden's tower acting as a campanile to the cathedral of Allen's main titanium and glass exhibition hall, plus an egg-shaped Imax cinema building, also clad in titanium, playing the role of chapter-house to one side. They all work very well together, but the strange fact is that the tower is an older design that was originally meant to be somewhere else entirely.

Horden won a 1992 competition to build a new Glasgow landmark at St. Enoch's Square, in the city centre. The ingenious rotating tower idea - it is aerofoil-shaped, and turns itself into the wind like a windmill so as to cut down air resistance - was just what was needed to keep up the momentum Glasgow had gained during its City of Culture triumph in 1990. But the economic recession of the time put paid to the idea for years, until the advent of the National Lottery and the birth of the Science Centre.