Basel is pleasant year-round, but the standout event is the Basel Carnival (Basler Fasnacht), which starts at 4 am on the Monday after Ash Wednesday — precisely when the rest of Europe stops celebrating. Lanterns, fife-and-drum bands, and masked processions fill the old town for three days. It is one of the biggest carnivals in Switzerland and a genuinely memorable experience.
Summer brings the Art Basel fair in June, one of the world's most important contemporary art events. The Rhine is swimmable in summer and locals float downstream in waterproof bags — a uniquely Basel tradition.