One of the six craters of Maly Semiachik volcanic massif is filled with a turquoise-blue acid lake. A bath in it would be deadly due to sulfur vapours rising from its bottom and mixing with the lake’s water, thus making the mixture into a corrosive acid. The crater is 140 metres deep, with a constant water temperature of around 40 degrees Celsius and a pH level of 0.4. (aerial view)