Käsmu is at its best from June to early September. Long northern daylight, water warm enough to swim from late June, and the village fully open. The annual Viru Folk music festival in mid-July is the busiest weekend of the year — book accommodation well in advance — and is the only time the village really feels crowded.
May and September are good shoulder months: cooler, quieter, with the forest in fresh green or autumn colours. From November to March most of the village is closed: the maritime museum runs reduced hours, the cafés shut, and the bay can freeze over. The pine forest in deep snow is magical if you have your own transport and warm clothes; the boulder coast looks completely different under a sheet of sea ice.