The second half of the 20th century was unkind to Colchester. First it was obliterated in print by George Orwell, who had an atomic bomb destroy the Essex town in his most celebrated work, 1984. Then the planners arrived, and wrought some real damage. As in other English locations with deep Roman roots, such as Chester and Canterbury, they decided that the best way to improve the town was to build a ring road that claws deep into the civic fabric, allied with a bus station nudging against the ancient walls.
After such desecration, it is easy to conclude that Colchester has given up on tourism. The Cadogan Guide to England asserts that "despite a long history, its charm is confined to the High Street". At the top of this broad thoroughfare, a sign points the way to the Dutch Quarter. You might be tempted to follow the arrow, fondly imagining it will take you to the tangle of lanes created by craftsmen from the Netherlands who made Colchester a 17th-century centre of excellence for textiles. In fact, you will end up on Level 8 of the ugliest multi-storey car park in Essex (which, trust me, is saying a lot).
Somehow, Colchester managed to get itself twinned with the city of Avignon – the greatest glory of Provence. Les avignonnais must be baffled about how the marriage came to be arranged. Yet one of the most spectacular cases of mismatch in the annals of town twinning now looks a little less lopsided. The reason: the opening this week of Firstsite. This brave new structure transcends its utilitarian surroundings and seeks to become "a new social and cultural space for the East of England, taking you from Roman remains to very, very new work by living artists", according to the director, Kath Wood.
The Spanish city of Bilbao transformed its image thanks to what appeared to be a collection of offcuts from a Jumbo-jet factory, re-assembled in the shape of the Guggenheim Museum. Now Colchester hopes to repeat the trick, only with what look like gleaming copper remnants from the Guggenheim. The architect, Rafael Buñoly, has taken Colchester, architecturally, to places it has never been. He has coaxed the cladding – copper tempered with 3 per cent aluminium – into a flowing, golden crescent that juxtaposes itself between gardens and the ladies' toilet at the bus station. And bestows the town with a much-needed opportunity to shine, a chance taken up by many citizens on opening day last Sunday.
Firstsite's name reflects Colchester's status as the oldest recorded town in England, and the original Roman capital of Britannia. The centrepiece needs to be powerful to distract attention from all the shunting around in the adjacent bus station, and succeeds. Inside, the floor opens up to reveal the Berrylands mosaic.
This masterpiece, which once decorated the floor of a Roman townhouse, was discovered nearby but has never properly been shown to the public. Starting this week, every visitor has had the chance to be dazzled by the simple yet eloquent symbolism created a couple of millennia ago.
Andy Warhol's Oyster Stew can, part of his Campbell's soup series, was created only a couple of generations ago. What does this imported icon have to do with north-east Essex? The main ingredient. Ten miles away, the oyster beds of Mersea Island are among the richest in Britain.
Another artistic dimension that seems disconnected is a room full of 20th-century South American prints. These turn out to be from the University of Essex's vast collection of art from that region.
Throw in a trio of golden bicycles, a miscellany of municipal publications and a striking grove of palms created by Ai Wei Wei and there's a good chance your senses will be stretched.
Firstsite has imposed itself impressively on the map of Colchester. Can it help put Colchester back on the map of attractive towns to visit? Not quite in the same way that the bigger and costlier Guggenheim has done for Bilbao; unless I missed them, Colchester has no gorgeous main square in the old town lined with tapas bars nor a cathedral of heroic dimensions.
Yet artistically inclined visitors can now combine Firstsite with the bucolic charms of Dedham Vale and Flatford Mill. "Constable Country" lies about 20 miles north of Colchester, and remains unblighted by both reckless planning and atomic weapons.
Travel essentials: Colchester
* Firstsite (01206 577067; firstsite.uk.net) is a five-minute walk from Colchester Town station, which is served by trains from London Liverpool Street (faster services, and links from Norwich, use the town's North Station). The venue opens 9.30am-5pm daily except Sundays, admission free.
* To see the location on film, watch Simon Calder's latest travel video at independent.co.uk/firstsite