Hallasan is a shield volcano on Jeju Island of South Korea. Hallasan is the highest mountain in South Korea. The area around the mountain is a designated national park, the Hallasan National Park (Hallasan Gungnip Gongwon/한라산국립공원/). Hallasan is commonly considered to be one of the three main mountains of South Korea, with Jirisan and Seoraksan being the other two.