THE ONE BASILICA
This might just be the most spectacular, most beautiful and most intriguing building in the world: La Sagrada Familia, Antoni Gaudi's still unfinished masterpiece, a place of worship that is itself worthy of obeisance. There are so many architectural styles, so many forms, so many influences and so many unique attributes to this one basilica, due for completion in 2026, as to make it impossible to sum up in a few sentences. Just, see it.
THE ONE MARKET
No, it's not La Boqueria, the tourist-filled foodie haven on La Rambla. It's not Santa Caterina either, though this neighbourhood location makes a great alternative to the Boqueria crowds. Barcelona's best market is the Mercat de Sant Antoni, which has reopened after extensive renovations and features 235 establishments selling fresh food, restaurant bites and various other snacks and supplies.
THE ONE TAPAS BAR
Quimet y Quimet is no secret: this hole-in-the-wall tapas joint is usually filled to bursting with hungry diners day and night, food fanatics who are drawn here by the high-quality local canned seafood, the inventive tapas plates, the delicious "montaditos", or small sandwiches, the cosy room and the warm welcome. This is the quintessential Barcelona tapas bar, and it's a must-visit.
THE ONE MUSEUM
Those prepared to put up with long queues in the warmer months will be rewarded with a comprehensive tour of the early life and works of Pablo Picasso, one of Barcelona's favourite sons. The Museu Picasso de Barcelona holds an impressive collection – more than 3800 pieces – that include the artist's drawings made during his youth in the city, extending through to his "Blue Period" in the early 1900s.
THE ONE PARK
Antoni Gaudi's iconic work can be seen throughout Barcelona, most famously at La Sagrada Familia, but also at Park Guell, a charming space on Carmel Hill that dates back to 1926. The park features plenty of Gaudi's signature playful modernism, mostly inspired by nature: extensive mosaic work of various animals; twisting rock pillars that look like tree trunks; and park lands that are a pleasure to stroll and relax in.
THE ONE VIEWPOINT
The journey to Barcelona's Tibidabo amusement park is one that goes up, but also back. This charming little fairground is set atop a peak 500 metres above the city, and it's a throwback to another time, when cutting-edge rides took the form of carousels and Ferris wheels and little planes on long steel arms. There's a lookout at Tibidabo that takes in Barcelona in its entirety, and it's a spectacular place for a photo.
THE ONE RESTAURANT
More than 20 years ago, the Catalan restaurant El Bulli, helmed by famed chef and Barcelona native Ferran Adria, reinvented the idea of fine-dining as we know it. Though that restaurant has since closed, Ferran and his brother Albert now run a whole slew of eateries in their home city, including Tickets, a whimsical meeting of traditional tapas culture and molecular gastronomy.
THE ONE STADIUM
Forget Gaudi, Picasso and even the Adrias: Barcelona's most popular modern-day artists are those who lace up their boots and take the field at Camp Nou, the colossal, 99,000-seat football stadium in the Les Corts neighbourhood. FC Barcelona's home ground is a thing of beauty, and even when there are no games on (or you can't get tickets) a tour of the facilities is worth the journey to experience.
ONE MORE THING
If you happen to be in Barcelona between mid-November and April, be sure to seek out calcots: long, sweet onions that are roasted over open flames, then steamed and served with rich, nutty romesco sauce. This is a Catalan specialty, and a "calcotada" – the meal built around the onions' consumption – is a cultural experience that's not to be missed. You'll find calcots in many traditional, local restaurants.