Luleå has two distinct personalities depending on the season. Summer — particularly July and August — brings warm temperatures (often around 20°C), the midnight sun, and the archipelago fully open for boating. The city's summer festival, Luleå City Festival, takes place in July and draws large crowds to the waterfront. This is the most comfortable time for most visitors, though Gammelstad is worth visiting year-round.
Winter, from December through March, is cold (expect -10°C to -20°C, sometimes lower) but has its own appeal. The northern lights are visible on clear nights from late August through March, and the frozen bay offers ice roads, skating, and winter hiking. The period around the winter solstice (late December) is very dark, with only a few hours of twilight at midday. Spring (April-May) can be wonderful, with dramatic ice breakup and long bright days returning quickly.