Stóragjá is a little-known rift in north Iceland which holds cave filled with naturally-heated geothermal water.
Found next to the village of Reykjahlið, which sits against the popular Lake Mývatn, it is often overlooked for Grótagjá cave, as this feature was shown in Game of Thrones. Regardless, it is well worth the visit and has far fewer crowds.
To reach the azure geothermal waters requires visitors to navigate down a very tight ravine, then clamber into the cave using the ropes and carved steps provided.
Bathing in Stóragjá is highly discouraged, however, as its beautiful blue colouration is due to dangerous algae. Because of its lack of filtration, it also has unhealthy levels of bacteria such as e-coli from previous bathers.