Still unfinished more than 140 years after construction first began, the great Modernista Antoni Gaudí’s Sagrada Família is Spain’s most-visited monument, welcoming 4.5 million arrivals each year. Despite the crowds, this is an unmissable Barcelona highlight. A feast of sky-reaching towers, intricate sculptures and flowing nature-inspired shapes, the basilica commands attention from across the city, and is a favorite local discussion topic.

Work on the basilica began in 1882, but Gaudí only saw a small portion completed before he died in 1926. All told he spent 43 years of his life on La Sagrada Família, considering its creation a holy mission and even contributing his own funds. Considered his magnum opus, the Temple Expiatori de la Sagrada Família (Expiatory Temple of the Holy Family) was envisioned as an immense cathedral with 18 towers representing Jesus Christ, the Virgin Mary, the Four Evangelists, and the Twelve Apostles. The three facades (Nativity Facade, Passion Facade and Glory Facade) illustrate the life, death, and resurrection of Christ.

As you step into the basilica’s soaring interior, a forest-like feast of extraordinary leaning pillars emerges, bathed in calming yellow, blue, red and green light thanks to the stained-glass windows. The whole space is transformed into a rippling canopy, just as Gaudí planned. Despite starting construction in 1882, Gaudí's grand vision for the Sagrada Família remains unfinished more than 140 years later. The anticipated completion date is 2032 for the basilica's 150th anniversary, though this timeline has faced delays.

Sagrada Família is Barcelona's top attraction so expect crowds, but weekdays are often calmer. Bear in mind that this is a Catholic building; see-through clothing isn’t permitted, and skirts and shorts must be at least mid-thigh. The best way to dive into La Sagrada Família is on a guided tour; they run in various languages and take 50 minutes. The big highlight is a tour up the towers of the Renaissance or Passion facades by lift and stairs (other towers will be added as construction continues); you can also visit the towers independently with a ‘Sagrada Família & Towers’ ticket. All tickets and tours must be pre-booked online up to two months ahead, and include a downloadable audio guide.

The fact that the project was abandoned in 1914 does little to diminish the magic of Gaudí’s wondrous, Unesco-protected Park Güell, where the architect’s passion for flowing nature-inspired forms was elevated to new heights. It was here that Gaudí spent the last 20 years of his life, and the ingenious interplay with the natural world makes it unique.

In 1900, when Eusebi Güell commissioned an England-inspired ‘garden city’ for wealthy barcelonins, this area was still a tree-lined hillside outside Barcelona. Gaudí created two gatehouses, an undulating plaza, monumental steps and around 3km of pathways before the whole thing was called off.

Today, its fragrant slopes are awash with pine and olive trees, rosemary, lavender, wisteria and more. The curving, showstopping 1914 Banc de Trencadís by Josep Maria Jujol presides over the Plaça de la Natura; it’s flanked by the Pòrtic de la Bugadera (Laundry Room Portico), a cloister-like gallery of twisted stone columns. Then you reach the Sala Hipóstila (Doric Temple), with its forest of 86 angular stone columns. The curvaceous, spired Casa del Guarda is now a museum; the Casa-Museu Gaudí, where Gaudí lived, was built in 1904 by Francesc Berenguer.

Prebook your tickets to ensure you get in. The northern part of the park (the zona forestal) is open to everyone for free.

The Museu Marítim is located in the Gothic Reials Drassanes (Royal Shipyards) in Barcelona. This extraordinary piece of civilian architecture, built in the 13th century, is part of the city's rich maritime past. The Museu Marítim houses exhibits related to Barcelona's naval history, including old navigation charts, fishing vessels, and dioramas of the city's waterfront. The centerpiece of the museum is a full-scale replica of Don Juan de Austria’s 16th-century flagship. Don't miss the replica of the Ictíneo I, one of the world 's first submarines, invented in the 1800s by Catalan polymath Narcís Monturiol.

The museum also holds interesting temporary exhibitions. On some Sundays, access is allowed to the attached Jardins del Baluard and the 13th-century city walls.

In the early 1900s, a collection of unmatched Romanesque religious frescoes was rescued from rundown churches across northern Catalonia by the Stefanoni brothers, Italian art restorers who brought with them the secrets of strappo (stripping of frescoes from walls). Now these masterpieces are the jewels of Barcelona’s unmissable Museu Nacional d’Art de Catalunya (MNAC), set within the spectacular neo-baroque Palau Nacional on Montjuïc.

Many of the frescoes come from the Vall de Boí in the Pyrenees, including the standout Christ in Majesty from around 1223 CE (taken from the apse of the Església de Sant Climent de Taüll) and the Virgin Mary and Christ Child, done around the same time (at the nearby Església de Santa Maria de Taüll). They’re all displayed in meticulously recreated churches, giving the feel of how they would have looked in situ over a thousand years ago. Beyond the Romanesque frescoes, the museum holds many other treasures. Opposite the Romanesque collection on the ground floor is the museum's Gothic art section. The Gothic section includes striking works by Bernat Martorell and Jaume Huguet, and there are pieces by Diego Velázquez, Francisco de Zurbarán, Josep de Ribera, Francisco Goya, Tiepolo, Rubens, El Greco and Canaletto in the Renaissance and baroque gallery. On the top floor, beyond the beautiful domed hall with a Miró mosaic, don’t miss the 2021-opened Spanish Civil War rooms, which shine a light on this dark period through poster art, painting, photojournalism and more. The museum offers fine views across Barcelona from its terrace.

Designed by boundary-pushing architects Enric Miralles and Benedetta Tagliabue to replace its 19th-century predecessor, Mercat de Santa Caterina is one of Barcelona’s most entrancing markets.

Completed in 2005, the market is distinguished by its undulating, colorful ceramic roof made of tile shards in the Modernista tradition. The design originated from a photo of a fruit and vegetable stand, enlarged to a huge scale. Inside, bustling stalls sell produce and ingredients. Among the towers of tomatoes, bunches of herbs and tempting cheeses, Olisoliva stocks quality olive oils from all over Spain. Take a break at the locally loved market kitchen Bar Joan, where you can sit at the counter and dig into arròs negre (cuttlefish-ink rice) or the menú del dia. On the southern side, excavated ruins of a monastery that stood here from the 11th to the 19th centuries are visible.

Now, the market is an emblematic landmark, demonstrating Barcelona's continued spirit of architectural innovation. A great way to learn about the market and its forward-thinking design is on a walking tour with Barcelona Architecture Walks, whose guides are all architects and architecture professors.

Museu d'Història de Barcelona is a fascinating museum that takes you back through the centuries to the very foundations of the original Roman city. Head below ground, under Plaça del Rei, where you can walk through 4-sq-km of excavated Roman and Visigothic Barcelona. There you can see the remains of public laundries, dyeing shops, fish-preserve stores, a 6th-century public cold-water bath and a factory for making garum. Next, you’ll come upon the remnants of a 6th-to-7th-century church and necropolis, and winemaking stores. Ramparts then wind upward, past the remains of the gated patio of a Roman house and the medieval Palau Episcopal (Bishops’ Palace).

Don’t miss the 14th-century foundations of Barcelona’s Gothic cathedral. You eventually emerge in the Saló del Tinell, the banquet hall where the Reyes Católicos (Catholic Monarchs) heard Columbus’ first reports of the New World. The finale is the Capella Reial de Santa Àgata, the chapel of the old Gothic Palau Reial Major (Grand Royal Palace). Outside, a spindly bell tower rises from the northeast side of Plaça del Rei. Inside, all is bare except for the magnificent techumbre (decorated timber ceiling) and the 15th-century altarpiece, considered to be one of Jaume Huguet’s finest surviving works.

One of the city’s most popular family-friendly attractions is the science museum CosmoCaixa. The single greatest highlight is the recreation of more than 1-sq-km of flooded Amazon rainforest (Bosc Inundat). More than 100 species of Amazon flora and fauna (including anacondas, colorful poisonous frogs, and capybaras) prosper in this unique, living diorama in which you can even experience a tropical downpour. Another unique exhibit is the Mur Geològic, a 24-meter-long wall assembled from 90 metric tons of rock showing different geological processes.

As you walk through the rest of the museum, you’ll learn about everything from fossils to physics, the alphabet to outer space. The 3D Planetari (Planetarium; €6 extra) is open at 5:30 pm on weekdays and for a varied range of sessions on weekends (check online). Aside from the Planetarium, many of the other exhibits are only in Catalan and Spanish. After your time in the museum, stroll through the extensive Plaça de la Ciència, whose modest garden flourishes with Mediterranean flora.