Ciutat Vella (Old Town) in October

April through June gives you the sweet spot — warm enough for outdoor dining, not so hot that walking on stone streets becomes torture. May particularly shines, with jacaranda trees blooming purple along the wider avenues and temperatures sitting comfortably in the low 70s. September and October work almost as well. The summer crowds thin out, but café terraces stay open and the Mediterranean still feels swimmable from nearby Barceloneta beach. October can surprise you with perfect 75-degree days. July and August? Look, the weather's gorgeous, but so is every other month here. The narrow medieval streets become human rivers, restaurant prices jump, and finding a quiet moment in the cathedral cloister becomes nearly impossible. If you must come in summer, book everything in advance and embrace the early morning hours. Winter brings fewer tourists and lower prices, but also unpredictable weather. December through February can dump rain for days, and while it rarely gets truly cold, the stone streets stay damp and slippery. But cozy up in a wine bar on Carrer de la Mercè, and winter suddenly feels romantic.