‘Now I know I’m in the Med.’ Carolyn smiled as she wiped her greasy fingers on the paper napkin. ‘How’s that?’ I asked.

‘Because I’m a hot mess!’ She looked down at her spattered top. ‘Remember when we were on the Greek islands and used to wear our clothes inside-out because they were so bad? Then Granada, when I flipped the pot of oil on the kitchen floor?’ Soon the four of us were laughing about all the great Mediterranean messes we’d shared over the years.

Our oldest pals Carolyn Steiner and Chris Malumphy had flown in from Cleveland, Ohio, to celebrate Carolyn’s birthday in Barcelona with Michael and me. It was February, and en route from the airport they had told tales of Cleveland blizzards and plane de-icings.

Dumping their bags at the hotel, along with their winter coats – it was powder-blue skies, light-jacket weather in Barcelona – we marched them straight to our favourite pit stop, La Cova Fumada. Pretty much unchanged since it opened in 1944 – chalkboard menu, no sign – it was the perfect antidote to their butt-numbing transatlantic flight, with aromas of fresh hot seafood lingering in the air. Sated, we surveyed a table even messier than Carolyn’s attire, strewn with the remnants of squid and sardines grilled with garlic, parsley and olive oil, pa amb tomàquet (tomato-smeared bread) and bombas: golden breadcrumbed mashed potato ‘bombs’ invented way-back-when by the owners’ gran.

So far so good, despite earlier misgivings – Chris had wondered whether Barcelona would fit the bill in winter, as we’d suggested. Neither of them had visited before. Might the Virgin Islands be better? he wondered.

Nonsense, we replied. (Not that either Michael or I had ever been anywhere near the Caribbean.) We knew Barcelona well, having written our first guidebook to the city in 1980. Back then, its symbol, the Sagrada Família church, was only a facade. But now, more than three decades later, Barcelona had changed a lot – into a razzle-dazzle city that looks like no place on Earth, thanks in part to the playful fabric left by Gaudí and other Modernista architects from the turn of the last century.

Even if it were to rain the whole time, there were museums to visit. But to ensure Carolyn had fun, Michael and I hit on a surprise: something you could only enjoy between November and March. Already we were counting the benefits of Barcelona beyond the summer hordes.

La Cova Fumada is in seaside Barceloneta, the 18th-century fishermen’s district. FC Barcelona flags drooped over rusting balconies, interspersed with lines of laundered underpants along its mini-Manhattan grid of narrow streets.

In summer they’d be heaving with people heading for the beach. Now only dozing cats opened one eye as we walked past.

On the vast curl of sand, there were just a dozen or so strollers. The winter Mediterranean was dark and mysterious, but calm; wispy clouds wrote hieroglyphs in the sky above Ricardo Bofill’s striking W hotel, which looked like a breaching whale on Barceloneta’s tapering spit – a reminder that the 21st-century city was hardly sitting on its laurels.

While Michael and I took arty photographs, our friends collapsed, jet-lagged, and were soon snoring con brio.

We nudged them awake when it was time to head out to the Sagrada Família, the church that dominates Barcelona’s skyline as memorably as the Eiffel Tower does Paris. Even now, in winter, there was a small queue for us to breeze past smugly with our advance-purchased online tickets, although it was nothing compared with the summer snakes of people around the block.

The Sagrada Família is simply the most ambitious – if not the most bonkers – building project in Europe, which makes it always fascinating to revisit.

Architect-genius Antoni Gaudí took it on in 1883 and became obsessed by it, his designs growing ever bigger until the day 
he absent-mindedly walked in front of a street car and perished.

For decades, nobody thought it would ever be finished, but with almost 25 years of global popularity since the 1992 Olympics, and all those euros flooding in from ticket sales, plans are to have it completed by 2026, for the centenary of Gaudí’s death.

Our friends were properly gob-smacked. ‘Cheese and crackers!’ exclaimed Carolyn, who saves stronger words for when she really means them.

Our necks ached from gazing up into the nave’s forest of sequoia-sized columns, branching into a mind-boggling network of vaults, tinted deep-green, blue and fiery red by sunlight streaming through the walls of stained glass.

Then we took the lift a dizzying 65m up the towers of the facade, for the eagle-eye view over the city. It was nippy up there, as clouds sped by, making the sunlight flicker on and off. Above us loomed the mother of all cranes, working on the central tower that, at 170m, will one day make the Sagrada Família the tallest church in the world.

Barcelona has long been impressing tourists like us: at twilight we took the Metro to the Plaça d’Espanya to show our friends another of our favourite things.

Espanya, one of the city’s main hubs, was as frenetic as ever, traffic swirling under illuminated arcades of the bullring with its flying-saucer roof, added when they replaced the toros with shops.

We strode purposefully towards the National Palace, home to the Museum of Catalan Art. We stopped midway up the steps at what looked like your everyday fountain, where around 100 people were milling about.

‘Ta-da!’ we exclaimed.

‘Huh?’ Carolyn and Chris looked quizzical, but a moment later, at exactly 7pm, Freddie Mercury and Montserrat Caballé came blasting through the loudspeakers (‘I had this perfect dream Barcelona!’) as the Font Màgica sprang to life.

Its jets of water constantly changed colours as they danced to one cheesy number after another.

When La Bamba came on, Carolyn let out a whoop and danced along with the fountain in proper birthday-girl fashion. We clapped madly at the end. In summer, when it gets dark later, you have to wait until 9pm for similar thrills.

One more plus for winter. Another was getting into our favourite restaurant without booking. Taberna La Parra was just a 12-minute walk from Plaça d’Espanya, in Hostafrancs district.

We ordered its wood-grilled T-bone steaks and morel omelettes in an atmosphere that grew increasingly jolly as Carolyn and a pair of young actors got into a knockabout discussion comparing Cleveland to Barcelona, Carolyn wowing them with her half-baked Spanish (imagine Fawlty Towers’ Manuel in reverse).

Next day was Sunday, and although we got up late, the medieval centre, the Barri Gòtic, still seemed lost in dreams under overcast skies. When finally we found an open restaurant, we stopped for coffees and spirally, light-as-air ensaïmada pastries that left us coated in powdered sugar.

The sun had just fought its way through the clouds when a tune came drifting from the Cathedral square. We hurried over to find a dozen musicians on wind instruments and a bass, with a large circle of people holding hands, tripping jauntily around a pile of coats and bags.

Every Sunday at noon, Barcelonans from all walks of life gather to dance the Sardana, the Catalan national dance banned for decades by Franco. In summer, tourists surround the Sunday Sardana with iPads and selfie sticks. In February, there were far more dancers than spectators. Carolyn, who loves a wiggle, was raring to join in as she used to do when we travelled in Greece, but I held her back, and whispered: ‘It’s a special Catalan thing,’ as their feet softly tapped, eyes closed, lost in their special Catalan zone.

‘Then I’ll just have to be reincarnated as a Catalan,’ she replied, entranced.

We went on to a few more special Catalan zones that afternoon: the Fundació Joan Miró, luminous and blazing with gorgeous blues, greens, reds, yellows and blacks (‘even his black is wonderful,’ Carolyn marvelled of the artist’s surreal strokes), and Park Güell, Gaudí’s technicolour wonderland.

Our friends didn’t want to leave, enchanted by the fairy-tale gatehouses, grinning lizard fountain and serpentine bench overlooking the distant city, sharply in focus in the crisp winter light. After a stroll through the park’s magical parabolic stone arcades, we sat watching squawking green parrots flit around the palm trees.

‘It feels like Munchkin Land,’ said Carolyn, whose party trick is knowing the entire Wizard of Oz by heart. She began singing Ding Dong! The Witch is Dead, with all the funny voices. Passers-by stopped and applauded when she finished. ‘Actually the whole city is a bit like Oz,’ she said. ‘The Sagrada Família could be the Emerald City if you squint, and that church on the hill...’

‘Tibidabo?’ Michael asked.

‘Yup. That could be the castle of the Wicked Witch.’

‘And you could be Dorothy,’ I added.

‘Well, Toto, we’re certainly not in Kansas any more!’

The next day was her big birthday, and time to spring our surprise. Armed with directions from a Barcelona friend, Mary-Ann, we took a train into the Collserola hills, which bear-hug the city, getting off at Sant Cugat del Vallès, and from there a 45-minute hike through the woods (sharpening an appetite is essential, Mary-Ann warned). All the while our friends kept guessing: were we leading them into the woods like Hansel and Gretel? Were we on a treasure hunt? Looking for truffles? At some stage Carolyn even began chanting: ‘Lions and Tigers and Bears: Oh My!’ – channelling her inner Dorothy again.

As the Masía Can Borrell, an old farmhouse converted into a restaurant, came into view, they were relieved that there was lunch at the end of the trail and not a witch. We were all famished. The big surprise? Onions – or to be precise, calçots, the stars of the classic Catalan winter barbecue known as the calçotada.

Amid Masia Can Borrell’s time-darkened beams, panelling and yellowed plaster, happy bib-bedecked diners lowered leek-y calçots into their mouths like sword swallowers. Our pals stared, then grinned – this was going to be seriously good fun.

The waiter brought platters of charred calçots and cups of garlicky sauce, tomato bread, chips and heaving mounds of grilled chicken and sausage. The people at the next table demonstrated how to strip the blackened leaves from the tender white stalk, before dredging the lot in sauce and dropping it down your gullet. We laughed and ate way too much. By the end we were completely covered in soot and sauce.

Winter Barcelona had left its mark beautifully on two first-time visitors – and all of us beamed when Carolyn declared with delight: ‘That was the best mess ever!’

Where to stay

W Barcelona (above) is a funky glass behemoth on the beach at Barceloneta (0034 93 295 2800, w-barcelona.com; doubles from Dh1,000 approx.).

Hotel España is an arty, Modernist pad (00 34 93 550 0000, hotelespanya.com; doubles from Dh500).

Hesperia Barri Gòtic is simple, stylish and central (00 34 93 310 5100, nh-hotels.com; doubles from Dh280.

Where to eat

La Cova Fumada, Carrer del Baluard 56 (00 34 932 214061).

Taberna La Parra, Carrer de Joanot Martorell 3 (00 34 933 325134).

Masia Can Borrell, Sant Cugat del Vallès (00 34 935 803632).

What to see

Sagrada Família (sagradafamilia.org; Dh59, or Dh118 with entry to the towers).

Font Màgica, Avinguda de la Reina Maria Cristina. Park Güell (parkguell.cat).

Further information, see barcelonaturisme.com.