Busan is a year-round city, but the season changes the experience significantly.
Summer (July–August) is when Haeundae Beach is at its most intense — at peak weekends up to a million people crowd onto the sand, umbrellas touching, lifeguards on platforms trying to see over the crowd. The water is warm and the nights are lively, but the city becomes extremely busy and accommodation prices spike.
Spring (April–May) and autumn (September–October) are the best times to visit. The weather is mild, the beaches are quieter, and the mountains around Beomeosa and Geumjeongsan are at their most photogenic. October is particularly good because of the Busan International Film Festival.
Winter (December–February) is cold but manageable — rarely below freezing for long, and the beaches and temples are almost deserted. Good for a peaceful visit if the cold doesn't bother you.
Busan International Film Festival (BIFF)
Asia's largest film festival, held every October in Haeundae and Centum City. Founded in 1996, it screens several hundred films from across the world over ten days, with a strong focus on Asian cinema. Industry screenings, premieres, outdoor events, and a generally festive atmosphere around the Haeundae waterfront. If you are in Korea in October, it's worth timing a visit around it — tickets are cheap and accessible, and the outdoor screenings on the Busan Cinema Center plaza are free.