After he swam the sub-freezing waters of the North Pole, Lewis Pugh vowed never to take another cold-water dip. Then, he heard of Mt. Everest's Lake Imja -- a body of water at an altitude of 5,300 meters, entirely created by recent glacial melting -- and began a journey that would teach him a radical new way to approach swimming, climate change, and pretty much any situation he comes across in the future. But one thing he hasn't changed his mind about is his belief that "very few things are impossible to achieve if we put our whole minds to it".