Hallasan, or Mount Halla, also called Yeongjusan Mountain, is Korea's tallest mountain, 1950 meters. It has not been an active volcano for 1000 years. It has many rock formations, a crater lake full of islands, and many cliffs and waterfalls. Over 1800 types of plants live on the mountain and 4000 types of animals, including 3300 species of insects.