The Grand Korean Waterway, officially known as the Pan Korea Grand Waterway, was a proposed 540-kilometer-long (340 mi) canal connecting Seoul and Busan, South Korea's two largest cities. The canal would run diagonally across the country connecting the Han River, which flows through Seoul into the Yellow Sea, to the Nakdong River, which flows through Busan into the Korea Strait. The proposed canal would traverse difficult mountainous terrain.