ARCHITECTURE: The art of conjuring new tricks out of old buildings

They try, oh how they try, but most modern architecture is still no place for art, despite the work of so many honest brokers trying to connect the two. On the one hand there are those buildings - by the likes of Sir Norman Foster - complete in every detail, that need artworks to animate them like Chartres needs double-glazing. On the other, there are those new buildings, tweedy, "vernacular" and bothersome, that are made only messier when touched by the hand of painter or sculptor. In any case, so much contemporary art is self-contained, or a law unto itself, that all it demands of architecture is four white walls, air-conditioning and enough light to be seen and experienced - which is why many new galleries are no more than the sum of these parameters.

When involved from the start of a building project, artists can work beneficially with architects (as in the new extension of St John's College, Oxford, where the talents of Alex Beleschenko, a glass artist, and Wendy Ramshaw, a jeweller, have dovetailed with those of the architects MacCormac Jamieson and Prichard), but such projects are still rare rather than the norm.

Under the soubriquet Artangel, James Lingwood and Michael Morris have spent several years inverting this fraught art-into-architecture equation. They have made architecture the subject of art and allowed the artist to transform existing buildings or create buildings, even if temporarily. In doing so, they encourage us to experience architecture in new ways, freed from function.

Artangel plans one major art-into-architecture event a year. Last year it hit the jackpot with "House", a full-sized plaster-cast of a Victorian terraced house in east London, made by the artist Rachel Whiteread, who went on to win the Tate Gallery's controversial but coveted Turner Prize. As with all Artangel projects, "House" was meant to be a passing phenomenon, an installation outdoors, as it were, to be enjoyed, recorded and demolished.

But the work drew such crowds and such loyalty that when the local authority insisted on its demolition it was castigated for cultural philistinism and denounced by the loud and lofty of the cultural highlands.

"House" went all the same, which was right. Its very impermanence, despite what Rachel Whiteread said at the time, was why it mattered. Still, it was delightful for Lingwood and Morris to see so many aesthetes, who only Hackney knew (because Hackney rolls out artists by the barrelful), making their way into the East End's art of darkness.

Artangel's latest temporary project, "Running Time", by Tatsuo Miyajima can be found in one of the most enduring British buildings, the Queen's House, Greenwich (1617-37), which was designed by our first classical architect, Inigo Jones.

Jones, the son of a Smithfield clothworker, was a radical architect, painter and celebrated designer of masques. The Queen's House was never less than a theatrical enigma behind its chaste Palladian mask: two blocks comprising three cubes linked by a bridge with the London to Dover Road running below. The centrepiece of the southerly block was a hall 40 feet high, 40 feet wide and 40 feet long, with a gallery running round it. It is from here that, over the past fortnight, visitors have peered, puzzled and enthralled, at Miyajima's new installation. Sadly, it is impossible to reproduce the experience of "Running Time" in a newspaper photograph.

Taking the passage of time as his theme (Greenwich, of course, is where official time, or GMT, begins and ends), the artist has blacked out the windows and set time (red, digitalised and ever-changing) coursing round the floor of the perfectly proportioned hall on the back of tiny, invisible electronic dodgem cars. Time is represented as a kind of hypnotic chaos, a lovely conceit in a building where absolute and permanent mathematical ratios and proportions rule.

Where Jones's work is, in part, an artistic play on the nature of mathematical perfection and the Platonic Ideal, Miyajima's installation is a celebration of randomness and time. It is mesmerising, evidently popular and rather beautiful.

Artangel's next production is "Selfstorage". Brian Eno and Laurie Anderson will design what promises to be a weird and wonderful installation, making much use of sound, inside a self-storage depot next to Wembley Stadium.

For Morris and Lingwood, variously described as "cultural entrepreneurs" and "arts producers", Artangel is a part-time occupation. Funded by the Arts Council and London Arts Board and sponsored by Becks beer, Artangel has drawn sizeable audiences to places that havebecome hackneyed or have never been on the arts map. They have brought thousands of people, who would never step into the haughty world of London galleries, into contact with avant-garde installation, landscape and performance art. Lingwood and Morris are truly on the side of the angels and performing minor miracles that everyone with an eye and a soul can appreciate.

`Running Time' is at the Queen's House, Greenwich, until 5 March. Entrance is free.