Barcelona, and the basilica that never quite arrives

In June 1926, Antoni Gaudí was knocked down by a tram on his way to evening prayers. He was dressed so plainly, by then, that the cab drivers who might have taken him to hospital assumed he was a beggar and left him where he lay; he died three days later, and was buried in the crypt of the church he had spent the last decade and more of his life designing and had known, all along, he would not live to finish. A century on, the Sagrada Família is still not finished. It is, at the time of writing, the longest-running construction project most visitors will ever walk into.

That fact tends to be treated as a curiosity, a bit of trivia for the queue. It is better understood as the key to the whole city. Barcelona does not demolish its awkward, unresolved history and start again; it builds around it, over it, and occasionally straight through it, and the result is a place where several centuries sit in view of each other without much apology.

A grid with the corners cut off

Walk out from the Gothic Quarter, where fragments of the Roman wall of Barcino still stand between tapas bars, and the medieval tangle gives way abruptly to the Eixample, the vast grid of streets laid out from 1859 by the engineer Ildefons Cerdà to relieve a city that had outgrown its walls. Cerdà's grid has one quiet oddity that first-time visitors often notice without quite placing: every block has its corners sliced off, an octagonal shape repeated for kilometres in every direction. He designed it that way for light, ventilation and, not incidentally, so that trams could turn the corner without demolishing anything. It is the sort of decision that looks eccentric until you understand the problem it solved.

Gaudí built several of his most famous works inside that grid rather than apart from it: Casa Batlló and Casa Milà, better known as La Pedrera, sit on the Passeig de Gràcia among perfectly ordinary apartment blocks, their curved stone and iron balconies looking, from a certain angle, like buildings that are still slightly molten.

The church he knew he would not see finished

The Sagrada Família itself was begun by another architect entirely; Gaudí took over the commission in 1883, still in his early thirties, and progressively abandoned every other project to give it the rest of his life. He raised funds for it door to door in his final years, and left behind plaster models and drawings, many later destroyed in a fire during the Spanish Civil War, from which later architects have had to reconstruct his intentions rather than simply follow a finished plan. Building continues today using techniques, computer modelling among them, that Gaudí could not have imagined but whose logic, architects who work on it say, follows directly from the geometry he set down.

The effect, walking in, is not of a building interrupted but of one still arriving, tower by tower, a hundred years after its architect stopped being able to check on it in person.

A city with a beach it built for itself

Barcelona's seafront is younger than it looks. Before the 1992 Olympics, the coast at Barceloneta was mostly railway sidings and industrial waterfront, and the beach that now draws the city's evening crowds was created largely for the Games, opening a Mediterranean city back up to its own sea after a long stretch with its back turned to it. It is a reminder that Barcelona's reinventions are not confined to Gaudí's century.

For visitors arriving by cruise, a call here is usually a single day, enough for the basilica and a walk through the Gothic Quarter but not much more. Those who want longer usually go by land: Just You's Costa Brava tour uses Barcelona as its base for excursions to Girona and the medieval villages up the coast, while Explore's walking trip into the Pyrenees begins here before heading north to Andorra, trading Gaudí's curves for rather older and harder ones.

Whichever way you arrive, allow more time than you think for the Sagrada Família, and don't be surprised if the cranes are still up. They have been for longer than the city has had traffic lights, and nobody in Barcelona seems in any particular hurry about it.