Grjotagja Lava Cave

Grjótagjá is a small lava cave beside Lake Mývatn in north-east Iceland, where a vivid blue geothermal spring fills a rift in black lava. Locals bathed here for generations, but eruptions in the nearby Krafla system drove the water too hot, and swimming has been banned ever since — you come to look, not to soak. The cave is also where Jon Snow and Ygritte meet in Game of Thrones, but the steaming turquoise pool needs no screen credit.