Barcelona is a year-round city. The constraint is heat and ticket availability, not closed monuments. If Gaudí is the reason you came, avoid treating August as a bargain.
March–May and September–November
Pleasant walking weather, still-warm sea in autumn, and the windows when most travellers should book. Easter week is busy. September has fewer cruise-day spikes than July.
June–August
Hot, crowded, and peak hotel rates. Sagrada Família and Park Güell sell out furthest ahead. The beach helps; the Gothic Quarter at noon does not. Locals leave in August — some restaurants close.
December–February
Quieter, cheaper, and still walkable. You will not swim comfortably. Gaudí interiors are the same; the light is softer. A good city-break window.
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