Take an early-morning stroll through the misty streets of sleepy Zaragoza to the banks of the muddy Ebro and you’ll encounter something that will make you gasp. It’s nearly 900ft long, weighs 5,700 tons and lies flopped across the river like a giant, dozing lizard.

The Zaragozanos gape in its vast shadow, peering through the security fences, snapping grainy shots with mobile phones and trying to describe this alien object. Some say it looks like a beached submarine, others a crashed spaceship. A few tentatively suggest that it might be the British architect Zaha Hadid’s new bridge.

But the unsettlingly beautiful, wholly enclosed bridge-cum-art gallery is just a gateway to a whole new world of weirdness on the north bank of the Ebro.

In the distance looms a glass skyscraper with no internal floors, and an enormous, exploding cascade of metal, representing a drop of falling water, splashing onto one side. To the right, the first pale rays of the rising sun paint pink a vast dome of encrusted salt; further on, past the church-sized iceberg floating in the river, is a towering terracotta forest.

Zaragoza, home to Expo 2008

Zaragoza is thriving with its aquatic Expo 2008 but the city has much more to offer, says Martin Symington

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• Zaragoza, home to Expo 2008

It’s been a long time since there was a miracle in Zaragoza, a pretty town of churches, Roman ruins and some of Spain’s best tapas bars. The last big thing – the apparition of the Virgin Mary in AD40 – promised merely the salvation of the soul. Expo 2008 vows to save the world.

There’s faith here that this £1.7 billion event, billed “the biggest water festival on earth”, will bring about an international agreement on the management of the dwindling resource. It’s apposite that it should be located in the European nation most likely to become a desert, and ironic that it is happening in Aragon, on the banks of the Ebro: Spain’s current water war was sparked by the government’s refusal to divert the mighty river to drought-stricken Catalonia, and this national dispute brings into sharp focus the issues facing the rest of the world.

“Had you heard of Kyoto before the protocol?” asks Expo 2008 boss Eduardo Lopez-Busquets. “I’m hoping that, in future, when you think of water, of the moment when the world realised how precious it was, you will think of Zaragoza.”

He insists that Expo isn’t a theme park, but he’s wrong: it’s the most intelligent and inspirational theme park on earth, a flood of 5,000 shows spread over 104 national pavilions, ranging from Afghanistan to Yemen. As well as daily presentations by Canada’s Cirque de Soleil and Argentina’s De La Guarda, there’s a nightly performance by the Spanish company Focus on that giant iceberg, which cracks open, Transformers style, to reveal a giant, robotic face that’s part Homer Simpson, part Terminator.

Elsewhere in the park, Bob Dylan tops the bill on a gig list that includes Paul Weller, Robert Cray and Patti Smith, all at no extra cost.

And there’s water, water everywhere: dripping, splashing, trickling and hammering, cascading down the side of Europe’s biggest freshwater aquarium, meandering through the cathedral-like gloom of the Aragon pavilion and surrounding the Spanish pavilion like a moat. The architect Patxi Mangado says he got the idea for this wonderful building – an immense roof supported by hundreds of slender terracotta columns – from a Pyrenean forest.

It’s not just art and architecture, either. There are more than enough high-tech, scratch’n’sniff, sensurround, CineMax-style experiences here, from a walking, talking hologram of Leonardo Da Vinci to a terrifying hurricane simulator, to enthral the most jaded of teenagers.

Travel details: Expo 2008 runs from Saturday until September 14 and is open from 9am to 4am daily; www.expozaragoza2008.es. Admission costs £28 for adults and £17 for children under 14. Cable-car transfers from the railway station are £7 return; otherwise, take the E8 bus from the Plaza de España for 70p.

Ryanair (www.ryanair.com) flies to Zaragoza. Bus transfers from the airport to the city centre cost £4 return. The four-star Catalonia Plaza (00 34-976 205858, www.hoteles-catalonia.es) has double rooms from £175; or try the two-star Hotel Hispania (976 284928, www.hotelhispania.com), where doubles start at £136. And don’t forget to buy the ZaragozaCard (913 604772, www.zaragozacard.com), valid for one, two or three days and offering five, seven or nine free bus rides, a guided tour of the old city, a guidebook, a free drink and a tapa. The 48-hour card costs £15.

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