grjotagja, lava cave with crystal blue hot water spring, myvatn geothermal area in north iceland

area bath bathing bay blue cave cavern crevasse europe fissure formation game thrones geology geothermal grjotagja grotte hot spring hverarapara hverir iceland icelandic inside krafla lake landmark landscape lava light mineral mountain myvatn natural nature north outdoor pond reflection rock stone surface thermal tourism travel turquoise view volcanic warm water small crystal formations