“WELL, that sounds like a barrel of laughs! How can a theme as dry as ‘Water and Sustainable Development' be expected to lure six million visitors?” So wondered the cynic in me as I arrived in this summer's Expo 2008 host city. What I hadn't reckoned on was the alegría - the sheer high spirits - with which Zaragoza is buzzing as it shimmers into the world spotlight.

The ancient capital of Aragon may be only Spain's fifth-largest city, but it is in the throes of an extraordinary renaissance, with dazzling new buildings and a resurgent old town humming with activity.

Arrive at the new AVE high-speed train station and there are ski resort-style gondolas (shaped like droplets, naturally) to carry you to the Expo site on a meander of the River Ebro just outside the city.

I was bewitched by my first glimpse of the Bridge Pavilion, a covered precinct and pedestrian viaduct spanning the Ebro like a space-age version of Florence's Ponte Vecchio. The bland-sounding “Water Tower” turns out to be a mesmerising, transparent, 80m-high (262ft) whim of latticed steel and glass, with a base shaped like a drop of water.

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Water, water everywhere... There is boating on an artificial lake, and a water-flume amusement ride. At the Ebro's edge, the world's largest freshwater aquarium houses fish, amphibians and aquatic mammals in re-created habitats from the world's great river systems.

The daily Cirque du Soleil performance promises to feature “aquabats”, and by night there will be concerts ranging from Handel's Water Music (what else?) to a performance by Bob Dylan, who has recorded a new version of his 1963 classic A Hard Rain's A-Gonna Fall for the occasion.

But what about the serious theme of the exposition? More than 100 nations will strut their stuff at pavilions on the riverside site, organised into “eco-geographic” regions such as sub-Saharan Africa.China, for instance, will be “demonstrating the power of water” by showcasing the Yangtze Three Gorges Dam. Expo aside, Zaragoza is packed with surprises. Broad avenues lead to the historic Casco Antiguo (old town), a maze of tiny plazas and paved alleys lined with shops and bars.

What surprised me even more, however, was that Zaragoza is a Catholic pilgrimage destination on a par with Santiago de Compostela. The reason is the belief that the Virgin Mary appeared to St James the Apostle in AD40 while he preached by the Ebro.

Zaragoza is also an ancient university town. This means great tapas bars, the best along “El Tubo”, a series of passageways through the Casco Antiguo. This, I suspect, is where the city's heart will continue to beat long after Expo 2008 has joined the Romans and Moors in the annals of Zaragosa's history.

NEED TO KNOW

Where to stay

Hotel Silken Zentro (00 34 976 703300, www.hotelzentro zaragoza.com Central location, boutique ambience; B&B doubles from £175.

Oriente (203282, www.hotel-oriente.com). On the edge of the Casco Antiguo; B&B doubles from £76.

Where to eat

La Ontina (5 Joaquin Costa; 214575). Modern Spanish cuisine, served with arty flourishes. The hottest table in town, booking essential.

Tapas: Along El Tubo, try the garlic mushrooms at La Ballena Colorá, and ewe's cheese with violet jam at La Despensa.

Getting there Ryanair (0871 2460000, www.ryanair.com ) flies from Stansted to Zaragoza. By rail from London to Zaragoza via Paris takes about 15 hours. Fares from £142 with Rail Europe (0844 8484070, www.raileurope.co.uk )

More information Expo entrance: Open daily June 14-September 14; £21 a day or £42 for three days (www.expo zaragoza2008.es and www.zaragozaturismo.es).

Spanish Tourist Office 020-7486 8077, www.spain.info/uk

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