I worry about the dependence on a few lifts - there are no escalators, and it’s a long way up by stair - but that quibble aside, perhaps the only slightly uncertain note about the whole composition is a leftover from Williams’ original competition scheme. He had wanted the whole end of the building to be able to open up to the fresh air. Curators don’t like nature much, so this idea was dropped. However a memory of it lingers on in the form of a large rigid "sail" at the eastern end. This can shuttle on rails from side to side to keep the morning sun off the exhibition floors. It seems a bit superfluous: venetian blinds inside would do the job just as well, if less theatrically.

So what will Nordgren fill his 32,000 square feet of art space with? There is a lot of specially-commissioned art - the opening show includes Julian Opie and American artist Chris Burden’s giant Meccano scale model of the Tyne Bridge. But one floor of the building is climate-controlled to top standards. "We could put on an exhibition of Paul Klee or Leonardo if we wanted to," he says. "Or an artist could fill a floor with sound, or even a smell. It’s about using the space in clever ways." Filling a floor with sound? That would include the floorful of giant gongs by Catalan artist Jaume Plensa, which is nothing if not satisfyingly interactive.

Cleverest of all, perhaps, is the way Baltic has a guaranteed £1.5m a year of revenue funding from the Lottery for its first five years, plus other five-year grants and sponsorship pledges. Nordgren is financially free to experiment. Baltic looks very promising: architecture as open proposition.