Barcelona: The crowds are gone in December - and the locals like it that way

It was an exhilarating and faintly surreal sensation. Suspended in mid-air over Barcelona last week, I gazed down over the tops of palm trees and across an expansive panorama of cityscape, green hills and sea. The morning air was so remarkably crisp and clear that, among the tangle of urban life far below, I could pick out two striking modern landmarks: the Sagrada Familia, Gaudí's great unfinished cathedral; and the Torre Agbar, a funky and phallic office tower that was built in 2004 as the gateway to the city's revamped Poblenou neighbourhood and which looks not dissimilar to London's Gherkin. From the vantage point of my cable car, I felt as if I were king of Europe's most flamboyantly stylish city.

I also felt utterly alone. Eerily so.

I was the sole passenger not only in my wide-windowed cabin but on the entire Montjuïc cable system, newly renovated last year and running up and down the vertiginous district in the west of the city. Here and elsewhere in the ancient and ebullient capital of Catalonia, Barcelona as touristland was serenely empty.

At the Miró art gallery, near the cable-car station on Avinguda de Miramar, I saw five other visitors, and a good half-dozen attendants. On previous spring and summer trips, I had jostled for standing room in front of the engagingly playful abstract art of one of Barcelona's most famously creative sons. Now I revelled in the space, walking twice round some rooms for the sheer heck of it, and retracing my steps to favourite paintings. There was scope, as well, to appreciate the clever, light-filled building by Josep Lluís Sert, who was also the architect of Joá*Miro's own villa at Palma on Mallorca.

Moving down towards the centre of town, I made tracks to Gaudí's iconic Sagrada Familia, started in 1882 and currently with a projected completion date if 2026, the 100th anniversary of the architect's death (although many locals regard this as an extremely optimistic target). The cathedral's huge spindle-shaped towers were etched out against a perfect blue sky, while the barrage of construction cranes beside them attained a graceful elegance in the extraordinary light that morning. As I strode past the admission barriers, the long queues of previous visits seemed an unlikely memory. In the uncrowded, scaffolding-clad interior I could wander at will, with plenty of room to take in the amazing forest of columns, the astonishing vaulting and the kaleidoscope of stained glass now in place. And as I stepped out to the celebrated east façade, only a handful of visitors was standing in front of the weird and wonderfully carved stonework of Gaudí's nativity scene.

Meanwhile, the sun shone. By lunchtime, the temperature felt positively balmy. I made for one of the cafés that are dotted along Avinguda de Gaudí, just beyond the cathedral, and sat outside enjoying a plate of tortilla de patatas and watching the world go by. Why had I never before visited Barcelona in winter? The light is fantastic and the weather supremely pleasant, with slightly chilly mornings giving way to mild and sunny afternoons (although life cools suddenly and dramatically after sunset). What's more, this is a city best explored on foot, yet for much of the year, it is simply too hot to do so.

Heading south, it was now a pleasure to stroll along the boulevards of the Eixample district, the city's elegant, late-19th-century extension, which contains a wealth of Barcelona's distinctive Modernist architecture. Josep Puig i Cadafalch's ornate Palau del Baro de Quadres is at Avinguda Diagonal 373; Lluis Domenech i Montaner's splendid Casa Fuster (now the Casa Fuster Hotel) graces Passeig de Gracia at number 132. Gaudí's seminal apartment block La Pedrera is just down the road at Passeig de Gracia 92, while his fantastical and finely restored Casa Batllo, looking as if it has been magicked in from a fairy tale, nestles between other architectural gems at Passeig de Gracia 43.

Modernist to medieval: I had reserved the riches of Barcelona's old district for my last day. First off, I made for El Born, the trading centre of the city in the Middle Ages. Yet for all El Born's historic origins, a group of its most striking merchants' mansions now houses one of the city's most compelling modern art collections. The Picasso Museum opened in 1963 with the agreement and subsequent donations of the artist himself, whose family had moved to Barcelona in 1895, when Picasso was 14 years old.

I arrived on the dot of opening time and, for a pin-quiet half-hour, had the collection entirely to myself. Footsteps echoing, I felt a sense of ownership as I took in the highlight of the museum, the Las Meninas gallery, showing most of the 58 studies Picasso made of the well-known painting by Velázquez. I even found myself grimacing in irritation at the distant sound of voices along the corridor.

Shops were just starting to open as I took a short walk west to the ancient heart of the city, the Barri Gotic. Outside the Gothic cathedral (currently shrouded due to the ongoing renovation work), Barcelona's Christmas market was getting into full swing. Beside stalls selling poinsettias and bunches of mistletoe, there were booths heaped with logs that had been decorated with smiling faces. The "caga tio", a stallholder explained, is, in literal translation, a "pooping log" – traditionally kids beat the log with sticks and it poops out presents for them (subtly produced by the adults).

He laughed at my evident surprise and took me over to the market section selling nativity scenes. There, among the shelves stocked with cribs, kings, donkeys and more, he pointed out row upon row of little squatting men, in the act of defecation, with their trousers down around their ankles. That's the caganer, he said: the pooping man who always features somewhere in Catalan nativity scenes. We love our earthy traditions here, he explained, adding that the market is not really an event for visitors – it's a very Catalan fair.

At this time of year, he said proudly, Barcelona is reclaimed by its residents.