From May 22, Lisbon will be better to visit than ever. That’s when Expo 98 begins, and a city already loaded with anti-quities and treasures “dives into the future”, as the publicity puts it. Expo 98 will be the last great exhibition of the 20th century. Five huge pavilions - one including a gigantic aquarium - will spread out on a 70-hectare site by the sea, and more than 100 nations will take part. The theme is: “The oceans: a heritage for the future. ”

The Expo organisers have taken an industrial wasteland, which included some poor housing, oil storage tanks and an arsenal, and have spent three years transforming it into a brand new suburb running along five kilometres of waterfront.

Massive amounts of city and government money have gone into creating Expo 98, and the organisers are quite frank about covering only 80 per cent of their costs. They see longer-term economic benefits from the regeneration of a forgotten corner of Lisbon. Fifteen million visitors are expected, most from Spain, but also in serious numbers from Britain and Germany.

After visiting what is still an alarmingly wet building site (it has rained far more than usual in Portugal this winter) I believe that this Expo will have a great deal to offer. Some startling architecture is already in place. There will be a huge and imaginative aquarium, a cornucopia of information on the nature of the ocean and our role in preserving it, and insights into the history of a country emerging confidently from several centuries of inertia.

Fun seems to be guaranteed - on the walkways by the sea, in the gardens, by monorail, watching the World Cup on huge video screens, going to any of the 3,900 scheduled arts events, or simply drinking white port and eating cod as you’ve never tasted it in the panoramic restaurant of the Vasco da Gama tower. And there are more than 140 smaller national pavilions to mooch around.

The architectural interest starts even before you’ve paid to get into Expo (Pounds 14 for a day ticket, Pounds 28 for three days, and Pounds 7 for a night ticket). The Oriente station, which is shared by trains, tubes and buses, looks like a cross between a white forest and a cathedral. It is stunning to behold, even before the insertion of the thousands of panes of glass needed to keep the elements out. How it will function as a station remains to be seen, but its Spanish architect, Santiago Calatrava, has built something really extraordinary.

When you get in you might want to make for the most-hyped attraction first: the Ocean Pavilion, designed by the American Peter Chermayeff. This will be the largest oceanarium in Europe, with a huge open tank in which 15,000 creatures and 200 species, ranging from sardines to sharks, can be viewed from two levels.

Four smaller tanks create the ecosystem of the North Atlantic, Indian, Pacific and Antarctic oceans. The Ocean Pavilion, sensibly, will be a permanent, post-Expo attraction in Lisbon.

The aquarium has large concave glass windows giving the spectator the feeling of actually being in the ocean environment, so you’ll be able to stand within inches of a hammerhead shark, great barracudas and porcupine fish. Some of the fish are apparently already in the tanks, but when I was there I didn’t see any. A tank containing as much water as four Olympic-size swimming pools leaking sharks would certainly make a big splash, but I’m sure everything will be all right on the night.

However, Utopia was ready, or nearly so. This is a huge oval hall which will, for the duration of Expo, house a six-times-a-day dramatic spectacle, on the themes of the “dreams, myths and legends of the ocean”. There’s room for 15,000 people in Utopia under a beautiful domed roof. In the future it will house everything from rock concerts to basketball.

You might want something quieter after this, and more pavilions provide a chance to extend your knowledge. The Portuguese Pavilion has a concave concrete roof base which sags picturesquely. Inside, the exhibition tells the story of the country’s pioneering maritime adventures in the 16th century and the part they played in the development of modern civilisation. The Knowledge of the Seas Pavilion shows how men learned to build ships, to navigate and to dive beneath the waves. A great deal of wood has been used in its construction and so it may well be the most restful of the pavilions to visit.

The Pavilion of the Future examines the current state of the ocean and looks at how individual and collective attitudes will have to change if the seas are not to suffer further ecological damage.

There’s a current joke in Lisbon which goes: Q. “What is going to happen in the year 2000 in Lisbon?” A. “Expo 98.”

There is still a frightening amount to do, but the 8,500 workers currently employed should finish it on time. The beautiful mosaic pavements are lying there ready to appear once the mud has been scraped off them. The spectacular new 13-kilometre bridge, which leaps across the Tagus at the eastern end of the site, is already a feature of the skyline.

It looks as though Expo 98 will be an exciting dive into the future, a worthy way of celebrating the Year of the Ocean and not at all a bad way to spend nearly half a billion escudos.

Lisbon itself has over a million people and, like most cities, it has been victimised by the car. However, there are charming little trams, a basic tube system and excellent rail services to two delightful beauty spots outside the city: Cascais and Sintra. Cascais has beaches, a rocky coastline and in spring and autumn balmy sea breezes. Sipping a leisurely coffee on the seafront is an essential respite from the overload which can overtake even the most relaxed Expo visitor.

Sintra is a bit more strenuous. The train takes about half an hour and travels through some of Lisbon’s least attractive suburbs. But Sintra is a gem of a village - cool, green and in the foothills of the Serra de Sintra. The Portuguese kings knew a good thing when they saw it and built two palaces here. The Pal cio Nacional de Sintra, in the middle of the town, dates from the 14th century and is an eclectic mixture of styles, with a strongly Moorish flavour.

The Pal cio de Pena is on a peak above the town. It was built at the end of the 19th century by Ferdinand Saxe-Coburg-Gotha, the German husband of Queen Maria II, and cousin of our own Prince Albert. It’s a fantasy palace, painted daffodil yellow and strawberry pink. Despite its size it has a human scale and the German architect, Baron Von Eschwege, has made the most of the site by providing breathtaking views. A walk along the battlements of the old Moorish castle nearby is not to be missed.

After a day out of Lisbon you’re ready for the city streets again. Lisbon is small enough to walk round, but it is hilly. Clever use of bus and trams (as prescribed in the excellent Dorling Kindersley Eyewitness guide) will save your legs, but beware at rush hour. In one bus I travelled on there were sudden shouts and screams - very rare in quiet and slightly melancholy Portugal. A woman had been robbed of her purse and the thief had calmly got out at the previous stop. It was the only time I heard voices raised in the whole of my stay.

The Gulbenkian museum, a little way from the centre of Lisbon, is a must. This excellent, modern building houses a remarkable collection made by the wealthy British financier and industrialist Calouste Gulbenkian, who made Portugal his adopted country in later life. It has Rembrandt’s “Portrait of an Old Man”, Rogier Van der Weyden’s “St Catherine”, and an abundance of 19th-century French paintings. Gulbenkian also bought some fine English work, including Turner’s breathtaking “Sinking of the Minotaur”, and some delightful Gainsboroughs and Romneys.

Back to sightseeing, the Alfama is a picturesque, steeply-sloped collection of tiny streets clustering around St George’s castle to the west of the city. A bit beyond it, on the way to the Expo site, is the azulejo (ceramic tile) museum - relatively small but full of vibrant colours and patterns and a reminder of how central tiles are to Portuguese culture. They make practical as well as decorative exterior surfaces for houses: waterproof in winter, cool in summer.

On the city’s eastern flank there are two notable sights that link well with Expo. The Discoveries monument, built in the shape of a huge sail right by the Tagus, features all the great explorers - led by Prince Henry the Navigator and followed by da Gama, Pedro Alvarez Cabral, the discoverer of Brazil, and by Ferdinand Magellan, who crossed the Pacific in 1520. Created by the Salazar dictatorship in 1960 it also celebrates more or less anybody who was anybody in Portuguese history and culture.

The Torre de Belem is a squat little tower which was in the middle of the Tagus when it was built in 1515 but is now by the shore. The great Portuguese sailors set out on their voyages from here. It was built as a fortress, but its glory is its exterior decoration: a rhinoceros appears in the design, rope motifs abound, and the battlements are shaped like shields.

It’s the work of a wealthy, self-confident nation. Five centuries on, and with the help of Expo 98, I could sense that confidence again.

* Contact the Portuguese Tourist Office for further details and advice on accommodation, 0171 494 1441

* Flights: TAP Air Portugal on 0171 828 0262, fax 0171 828 1742

* Further information: Web site: http:www.expo98.pt

* e-mail: infoexpo98.pt