Karlovy Vary in June

May through September gives you the best weather for wandering the colonnades without freezing. July and August are peak season — expect crowds around the major springs and higher hotel prices. But the energy is infectious, with street musicians and outdoor concerts almost daily. September is the sweet spot: warm days, fewer tourists, and the surrounding forests start their autumn color show. The Karlovy Vary International Film Festival in late June/early July brings Hollywood stars and serious people-watching opportunities, but book accommodation months ahead. Winter has its charm if you're into the whole romantic-spa-in-the-snow vibe, though many outdoor activities shut down. Spring can be unpredictable — I've seen snow in April and 25°C days in March. The thermal springs flow year-round at a constant 72°C, so that part never changes.