Lying between Greenland and Iceland, the Denmark Strait was crossed for the first time by theVikings in the late 10th century, during Erik the Red’s expeditions. In the Second World War, its waters were the theatre of a battle between the Kriegsmarine and the Royal Navy, on 24 May 1941. In the wintertime, extremely dense pack ice forms along the Greenlandic coasts and, while the Transpolar Drift sweeps icebergs along throughout the year, the strait is generally clear of ice during the summer. In the depths of the strait lies the world’s largest waterfall, an undersea cataract formed by the difference in temperature between the cold waters of the Greenland Sea and the warmer waters of the Irminger Sea. Numerous cetacean species thrive in this rich ecosystem.