What are the cities near the sea in Korea?

The capital Seoul is not far from the seaside. It takes more than two hours to get to the seaside by subway 1. Seoul's satellite city and Incheon, China's third largest city, are also near the sea. Jeju Island in the south is still near the sea. If you go to South Korea to see the sea, then the east coast of South Korea is better, and the environment there is very good. There are Busan and Pohang, the second largest cities in South Korea, in the southeast. There is Gwangju in the south. If traveling, I recommend the fast grass on the east coast (gangwon)