Vatnajökull National Park in November

Summer (June-September) offers the most access and 18+ hours of daylight. July and August are warmest but also most crowded - expect tour buses at Jökulsárlón. September brings fewer crowds and decent weather, but some high-altitude trails start closing. Here's the catch: ice caves are only accessible October through March when they're structurally stable. The famous crystal caves near Breiðamerkurjökull are at their most spectacular in November and December. Winter visits mean shorter days (4-6 hours of light) and harsh weather, but you'll have otherworldly ice formations and possible Northern Lights. Spring (April-May) is unpredictable - some years bring early melts, others extended winter conditions. Check glacier.is for current ice cave conditions before booking.