Nari Basin is a basin in Ulleungdo, South Korea, and is just under Seonginbong. The Nari basin is made by Seonginbong's past volcanic activity and is a caldera. Thousands of years ago, there was a huge volcanic activity in Seonginbong and after that, the underneath part subsided and the Nari basin was formed. The Seonginbong is now an extinct volcano and these days, people live in the basin and grow crops.