Hveragerði is accessible year-round and has genuine appeal in every season. Summer (June to August) brings long daylight hours — the sun barely sets in June — and the Reykjadalur valley is at its most pleasant for hiking, with dry trails and comfortable temperatures that make bathing in the hot river easy. The greenhouses are in full production, and the town has a lively if modest energy.
Winter visits have their own character. Steam rises dramatically from the geothermal vents against cold air and snow, and the Reykjadalur hike in winter, when the valley is white and the warm river cuts through the snow, is a striking experience. The Northern Lights are visible from Hveragerði on clear winter nights — being a small town, light pollution is minimal. The Ring Road is kept clear year-round, so access from Reykjavík is reliable in all but extreme weather.
Spring and autumn are the quieter shoulder seasons. The Reykjadalur trail can be muddy in spring as snow melts. Autumn brings reliable weather in September before the season turns, and the highland colours above the valley are good at that time.