In early 18th century the outlaw Jón Markússon lived there and used the cave for bathing. Until the 1970s Grjótagjá was a popular bathing site. But during the eruptions from 1975 to 1984 the temperature of the water rose to more than 50 °C. Today bathing is not possible anymore, though temperature is slowly decreasing and has fallen below 50 °C again. As alternative bathing site the nearby lava cave Stóragjá is being used.