After long—very long—winter nights, it"s not surprising that the First Day of Summer is cause for a big celebration in Iceland. The public holiday falls on the first Thursday after April 18, and launches Harpa, the first summer month of the old Norse calendar that was followed by the country"s first inhabitants. The year was split into just two seasons back then—summer and winter—which explains why Sumardagurinn Fyrsti, the First Day of Summer, falls in chilly April. Indeed, folklore has it that if you put a dish of water outside the night before the holiday and it freezes, you"ll have a good summer. Regardless of temperature, the holiday does herald the arrival of those famously long days with little darkness, a welcome relief after the light-deprived winter months.