If you want to get a taste of beach/coastal life in South Korea, you will definitely want to visit the city of GangNeung, which is about 3 hours drive from Seoul.
This coastal city GangNeung offers plenty of things to do with ski resorts nearby in the winter and also beach pampering for the hot summer. Personally, I avoid the busy summer times here as it can get very crowded but anytime else is a great time to visit and get some fresh, ocean air plus great Korean sashimi/seafood.
All along the coast of GangNeung, you will find fancy Korean seafood restaurants, jogging paths, hotels, and even WiFi on the beach. It’s a great place to get away from the city life in Seoul, which can become quite deafening after awhile.
On my trip here as seen in the video, I did go walk for miles along the coast, it’s a quite fascinating walk as you will find many nice coffee shops you can take breaks and admire the waves. There’s quite a few good waves to surf here although there’s not many surfers as it’s still new to South Korea. (In time, I am sure there will be more surfing opportunities out here though.)
And lastly but not least, GangNeung offers plenty of its own local Korean rice wine including JooMoonJin DongDongJu, that I highly recommend you to try at least once before leaving.