Mountainous Switzerland is another country known for its abundance of crystal blue lakes, including Lucerne, Brienz, and Oeschinen. We had a hard time choosing just one to add to our list but settled on the small yet striking Lake Blausee. Fed by underground springs, the lake is completely transparent, with a lovely blue-green colour. Sunken tree trunks and boulders are visible all the way down to the bottom 40 feet below. This is another lake seeped in legend: According to the tale, a broken-hearted, blue-eyed maiden drowned in the lake, and her tears turned the water its azure hue.