Tonight, at the forum …

If ever a city has managed to turn urban regeneration into a global tourist attraction, it is Barcelona. For the Olympic Games in 1992, Barcelona came up with one of the world's most glamorous collections of sports architecture and public spaces. The glamour concealed a more mundane municipal activity: the transient sports event served as a catalyst for regenerating a rundown industrial and port area of the city, including the reclamation of miles of coastline as parkland, marinas and sand beaches. Little wonder that in 1999 Barcelona became the only place (as opposed to person or practice) ever to win the top British award for architects, the Royal Gold Medal for Architecture.

Next week, Barcelona will again launch into an extravaganza of Olympian proportions that will combine a global event with the regeneration of another rundown industrial area. Only this time the event has nothing to do with sport.

Instead city officials have concocted something totally unprecedented. Forum Barcelona is billed as as "a rendez-vous to promote sustainable development and peace". This will take the form of a profusion of high-powered topical public debates and cultural celebrations, which like the Olympics will gather together celebrity performers and audiences from all over the world. From May to September, no fewer than 45 debates and conferences, 600 concerts, 1500 performances and 25 exhibitions will be staged.

To stage this global event, Barcelona has transformed the city's last obsolete industrial area into an extravagant forum complex at a cost of £220m. The 214 ha seafront site known as Besòs had been blighted by rundown port facilities and utility plants, and these have now been replaced by an array of leisure facilities in show-stopping architectural forms. Just like the Olympic site, but five times the area.

The centrepiece of the forum complex is the event's main 3200-seater auditorium designed by Herzog & de Meuron, the Swiss architect that currently basks in a near-unrivalled global spread of projects. This practice can be expected to come up with the unexpected, and the Forum Building is no exception. The 25,000 m² building is essentially a huge flat triangular slab that tilts up slightly from the ground. Its flat facades in dark blue cladding are slashed through with jagged irregular fissures that serve as windows.

The extraordinary design has a contrary logic to it, as explained by partner Jacques Herzog: "At first we wanted to do something tall. Later we said let's do the opposite – something flat. So it's like a piece of a city block that slopes down from the city to the sea. The auditorium is sunk into the plaza, and space below the upper end of the building is a sheltered extension to the plaza and is squeezed down to zero."

As for the triangular plan form, this was generated by Avenida Diagonal, one of the city's great avenues that, distinctively, cuts diagonally through the late 19th century gridiron of streets to arrive at the seafront site.

And the city's historic landscaped courtyards around the cathedral offered yet another inspiration, giving the building a naturalistic, if marine, character suited to its seafront site: "The facade is blue, like a sea sponge taken out of water," says Herzog. "And the flat roof will be covered in water, as we hope to attract migrating birds."

Alongside the main auditorium, the new forum site development contains a 68,000 m² convention centre designed by Josep Lluis Mateo, a marina, a seafront park and even an extended old people's centre. The buildings are set in a 150,000 m² plaza that is claimed to be the second largest civic space in the world, after Tiananmen Square in Beijing. Nearby, a polytechnic and 14 hotels are being developed.

And in a topical twist to regeneration, several old utility plants, which had been relegated to the marginal city site and included a power station and waste disposal site, have been replaced by modern utilities such as a solar power station and wastewater treatment plant. Not only are these at the cutting edge of sustainability but they form attractive and highly topical exhibits in their own right.

The biggest summer event ever, as its organisers call it, should attract more than 5 million visitors, who will not just come away culturally recharged and enlightened about the great social issues of the day. They will also have experienced the final chapter in Europe's most ambitious urban renewal project – and have helped pay for it too. The fact that the conference centre has already been booked up to 2010 suggests that, like the 1992 Olympic Games, Forum Barcelona will leave a legacy set to last well beyond the end of this summer's event.