Grjótagjá is a small water-filled cave that used to be a very popular bathing spot. Due to volcanic activity in the nearby Krafla, the temperature of the water has risen, making the water slightly too hot to bathe in. It is around 45°C, so you can get away with dipping your toes. Although the water might not be suitable for bathing, we still recommend that you explore this place as it truly is a beautiful spot, especially when the sun filters through the cracks in the roof and illuminated the interior of the cave.