Jökulsárlón Glacier Lagoon in July

May through September offers the warmest weather and longest daylight, but also the biggest crowds. July and August see tour buses rolling in every 20 minutes. For fewer people and dramatic skies, visit in May or September. The icebergs are actually more numerous in late summer as the glacier calves more actively. Winter visits are possible but challenging – the access road can close during storms, and you'll have limited daylight. But if you make it, the aurora borealis reflects off the ice in ways that'll make you forget how cold you are. Early morning visits any time of year mean better light and fewer crowds.