Castilian vs everywhere else
Spain's Spanish (Castilian) differs significantly from Latin American Spanish — vosotros conjugation, theta lisp on c/z, vocabulary differences. If your goal is European Spanish for travel or work, the city choice within Spain matters less; if Latin American Spanish, do not learn in Spain.
Salamanca
Salamanca is Spain's #1 language-learning city. Universidad de Salamanca (1218) issues DELE certifications. Don Quijote, AIP Salamanca, Mester schools. Compact medieval old town serves as classroom. Classical Castilian accent — clean, slow, learner-friendly.
Madrid
Madrid Instituto Cervantes, Don Quijote Madrid, Hispania, AIP Madrid. Standard Madrid Spanish — fast but clear. Big city advantage for cultural saturation. Less cheap than Salamanca but more variety. Malasaña youthful base.
Barcelona
Barcelona Don Quijote Barcelona, OnSpain, Camino Barcelona. Catalan-Spanish bilingual context: signs and locals' default Catalan. Less language-immersion-pure than Madrid. Coastal life compensates.
Sevilla
Sevilla CLIC Sevilla, Don Quijote Sevilla. Andalusian accent — fast, dropping consonants, drawing out vowels. Harder for beginners but more conversational practice with patient locals. Hot summers (avoid June–August intensive courses).
Valencia
Valencia Spanish Studio Valencia, Hispania Valencia. Beach-and-paella city; cheaper than Madrid; bilingual Valencian-Spanish situation. Mild year-round.
Strategy
Salamanca for serious immersion (4+ weeks); Madrid for shorter trips wanting big-city energy; Sevilla once you have intermediate base. DELE certification opens up TEFL Spain teaching jobs.