Grjotagja & the Icelandic lava caves

Iceland locked this one behind an iron gate, and the reason has nothing to do with geology.

Grjótagjá, crack in the rock, is a small lava cave near Lake Mývatn with a thermal spring inside it. Local lore puts the outlaw Jón Markússon here in the early 18th century, living rough and using the pool as his bath. English students rediscovered it as a bathing cave in 1938, and for the next forty years it was somewhere people simply went to soak.

Then the ground moved. The eruptions between 1975 and 1984 pushed the water temperature past 50 degrees Celsius, and bathing stopped in 1977. The temperature has been falling slowly ever since, and by 2005 it had come down far enough to sit in again for short periods, the way you would use a spa rather than a swimming pool.

That should have been the happy ending. Instead visitor numbers climbed and behaviour fell apart. The owners put up signs asking people not to bathe and to take their rubbish with them. People bathed anyway. They also washed their dishes in it, brushed their teeth in it, cleaned their shoes in it, carried glass bottles in, and used it as a toilet. In 2018 the owners fitted an iron bar gate and shut it.

You can still walk up, look through the bars and photograph the pool. It is free, self guided and unstaffed, with no lighting of any kind, so go in daylight. There are plans to reopen it properly for bathing one day with toilets and a warden, which is roughly what it needed all along. If you want to actually get in the water, Stóragjá nearby serves as the alternative.

It has one more claim on your attention. Grjótagjá was the setting for the love scene between Jon Snow and Ygritte in Kissed by Fire, the fifth episode of the third season of Game of Thrones. The waterfall in that scene was added afterwards.