Iceland
Best overall months to dive: Jan–Dec
Iceland's marquee dive is Silfra, a groundwater-filled fissure in Þingvellir National Park sitting on the boundary between the North American and Eurasian plates. It is a cold-water, drysuit, visibility-driven dive rather than a marine-life one: 2–4°C year-round and effectively no fish. Other Icelandic diving exists — the Strýtan hydrothermal chimney in Eyjafjörður near Akureyri, and the geothermally warmed lake Kleifarvatn on the Reykjanes peninsula — but we have researched Silfra first and will add the others later.