Pics show blue ice cave 'Devil's Hole' which forms every year in Swiss Alps

Several people on Wednesday visited a blue ice cave which forms every year at Glacier 3000 ski resort in Les Diablerets, Switzerland. The natural cave, also known as Devil's Hole, forms through siphon effect. Each spring and summer, the cavity fills with water from snowmelt, forming a lake. In autumn, the plug disappears and the water drains, leaving the cave.