It's not Hawaii, but we like it. DaeCheon Beach is a nice little beach on the west coast of Korea. It's easily accessible by train or bus for anyone from Seoul to Daejeon.
We have been going a few times a year for 8 years, and we always stay in the same place: Gaemi Chon Pension (개미촌) - literally, "Ant Village." But don't worry; we've never had problems with ants. It's a quaint little family run condo with about 8 private rooms and one small house for groups. The owner operator is a sweet old woman, and they always take good care of us. You can stay late if needed, and they will set up the barbecue grill for you any time you want it. Prices are very reasonable, and this is on the quiet side of the beach.
We always try to visit in the spring or fall. Summer can be kind of crowded unless you go on a weekday.
Also, don't forget to walk on past the ends of the beaches. On the north end, there is a quaint little fishing village, and you can pick up all kinds of sea glass on the rougher beach there. On the south end, you can hike over picturesque rocks with crashing waves.