Jeju Volcanic Island and Lava Tubes
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.