Grjótagjá is a small lava cave near Lake Mývatn in north Iceland, known for its stunning geothermal hot spring. Once used by outlaws and locals for bathing, it became famous as a filming location for Game of Thrones. Despite its beauty, the hot spring is now off-limits due to unpredictable geothermal activity. Visitors can still admire Grjótagjá's ethereal charm and explore the surrounding area on tours or self-drive adventures.