Grjótagjá

Where it sits. Grjótagjá is a small lava cave holding a hot spring, on the eastern side of Lake Mývatn in northeast Iceland, roughly two kilometres from the village of Reykjahlíð and reached by a short gravel spur off Route 860. It belongs to the fissure swarm of the Krafla volcanic system, a line of cracks running north to south through the district, and the fissure that contains it can be traced across the surface for hundreds of metres as an open gash in the lava. Two low entrances lead down into a chamber perhaps twenty metres long, where a flat sheet of clear, steaming water lies over a floor of dark rock. Rift walls above the cave give a wider view of the same fracture continuing across the plain.

The story behind it. The cave was a bathing place for local farms for generations, and Icelandic accounts connect it with Jón Markússon, an eighteenth-century outlaw who is said to have lived rough in the area and washed here. The water sat at a comfortable temperature for most of recorded memory. That ended with the Krafla Fires, the sequence of nine eruptions and repeated rifting events that ran from 1975 to 1984 a short distance north. Magma movement drove the ground temperature up sharply, and the pool climbed well above fifty degrees Celsius, hot enough to scald. Bathing stopped. The water has cooled slowly in the decades since, drifting back into the forties, but it is not stable, it can rise again without warning, and the landowners have kept the ban in place.

Access reality — read this before planning a swim. Grjótagjá is private property belonging to the farm at Vogar, and the family has been unusually generous in keeping it open, free, and unfenced beyond a low barrier and signage. What they ask in return is that nobody gets in the water. The prohibition is not a formality: the temperature is unregulated, the pool has no shallow entry, the rock underfoot is glassy and slick, and there is no supervision of any kind. Photographs circulating online of bathers in the cave are either historic or taken in defiance of the signs. Visitors who want to soak have two legitimate options a few minutes away — the Mývatn Nature Baths at Jarðbaðshólar, and the geothermally warmed pools in Reykjahlíð.

On screen. The cave is known internationally as the setting for one of Game of Thrones' most quoted scenes: Jon Snow and Ygritte in the third season, in the episode built around the line about knowing nothing. The Icelandic unit shot here in late 2012, and the location work captures the real entrances, the fissure and the steaming interior. The intimate water sequence itself was completed on a purpose-built set rather than in the pool, for the obvious reasons — the chamber is cramped, the rock is treacherous, and the spring is far too hot to sit in for a working day. It is a good example of how the series assembled a place: a genuine Icelandic cave for the establishing reality, controlled studio conditions for the performance.

What you actually see today. The approach is flat gravel from a small car park, and the site takes twenty minutes unless the light is good. The eastern entrance is the easier of the two, a scramble down over blocks into the chamber, where the water glows a saturated blue-green when sunlight finds the opening around the middle of the day. Steam condenses on the ceiling and drips. Neither entrance is remotely wheelchair-passable, and both are awkward in wet boots. Above ground, the walk along the open fissure is the underrated half of the visit: a straight-sided crack in the lava, in places wide enough to walk into, that shows exactly what plate-boundary rifting does to a landscape. Nearby Stóragjá, closer to Reykjahlíð, is a larger version with cooler, algae-clouded water and no safe access.

Getting there and timing. Grjótagjá sits about ten minutes by car from Reykjahlíð, on the loop that also takes in Hverfjall and Dimmuborgir; from Akureyri it is roughly ninety minutes on Route 1. There are no toilets, no cafe and no ticket desk, and the car park fills between eleven and four in summer when coaches work the Diamond Circle. Early morning, late evening under the midnight sun, or a winter afternoon with snow on the lava all give a far better experience. The gravel spur is usually passable in a two-wheel-drive car, but in winter it drifts over, and the last stretch can require care. Treat the site as someone's land, because it is.