Spain celebrates harder and more often than almost any country in Europe. Many festivals are deeply local — a single town's patron saint's day that draws the surrounding region — but a handful are internationally famous and worth planning a trip around.
Las Fallas (Valencia, mid-March) is five days of fireworks, massive satirical sculptures (called fallas), and a daily midday firecracker explosion called the mascletà. On the final night, almost all the sculptures are burned. Loud, smoky, and spectacular.
Semana Santa (nationwide, Holy Week before Easter) transforms cities across Spain with solemn religious processions, where brotherhoods carry enormous ornate floats through the streets. Seville's processions are the most famous — the combination of incense, candlelight, and saeta (flamenco lament) sung from balconies is unlike anything else in Europe. Málaga, Valladolid, and Zamora also have outstanding celebrations.
Feria de Abril (Seville, two weeks after Easter) shifts completely from solemnity to joy. A week-long fair with flamenco dancing, horse displays, and casetas (private tents) where sevillanas music plays from afternoon until dawn. Visiting without an invitation to a caseta requires some social engineering, but the atmosphere spills onto the streets.
San Fermín (Pamplona, 6–14 July) is much more than the running of the bulls. The week is a non-stop street party with music, dancing, and processions. The encierro (bull run) takes place each morning at 8am — watching from a balcony is safer and gives a better view than running.
La Tomatina (Buñol, last Wednesday of August) is exactly what it sounds like: a town-wide tomato fight, with over 100 tonnes of overripe tomatoes thrown in the streets. It sells out quickly; book tickets well ahead.
La Mercè (Barcelona, 24 September) is the city's main festival — free outdoor concerts, human towers (castellers), fire runs, and fireworks across multiple venues for several days.