Barcelona is usually planned around timed tickets and queues. It can be built almost entirely around things that need no booking, which is a better solo trip.
Book one thing
The Sagrada Família, first morning slot.
The interior is about light through coloured glass, and the morning eastern light through the nave is the strongest effect the building produces. It is also far quieter.
Single slots frequently remain when pairs are sold out — a date that looks full often is not, for one person.
Add Park Güell's monumental zone if you want the mosaic terrace. The wider park is free.
Day one: Eixample and Modernisme
Sagrada Família at opening.
Walk ten minutes to the Hospital de Sant Pau — Domènech i Montaner's pavilion complex in gardens, a UNESCO site, and almost empty. This is the Modernisme nobody queues for.
Afternoon on Passeig de Gràcia looking at the facades from outside, which costs nothing.
Evening in Gràcia — small squares, restaurants for residents rather than visitors.
Day two: Montjuïc
MNAC — Romanesque frescoes cut from Pyrenean church walls and reinstalled in reconstructed apses. One of the most important medieval collections anywhere and rarely busy.
The Miró Foundation on the same hill, in a building designed for it.
Down through the gardens, or the cable car across the harbour to Barceloneta.
Day three: the old city
The Gothic Quarter and El Born on foot, with no plan.
Santa Maria del Mar, free outside guided hours — fourteenth-century and austere after all the Modernisme.
MUHBA, where you descend into the excavated Roman city beneath the square.
Lunch at a market bar — Santa Caterina or Sant Antoni, counter seating, excellent food at counter prices.
Day four: the view and the beach
Bunkers del Carmel — a former anti-aircraft position with a 360-degree view to the sea. Free, bus and a short climb. Residents ask for quiet in the evening.
Bogatell or Mar Bella in Poblenou — quieter and cleaner than Barceloneta, a few metro stops out.
Eating alone
Market bars and tapas bars, where standing at the counter is the format.
Lunch menus at €14–18 in Gràcia and Sant Antoni, full of people eating alone.
Not the Ramblas.
Meeting people
Hostels in Eixample, El Born or Gràcia with common areas.
Free walking tour on the first morning.
Language exchange evenings, which run several nights a week in bars and are free.
Beach volleyball and running groups at Barceloneta, both of which take newcomers.
Practical
Pickpocketing on the Ramblas, the metro and at the main sights. Bag in front, phone away.
Most museums close Mondays.
May, June, September, October. August is hot and the city is at capacity.