Korea has thousands of islands but I do not know which ones are worth visiting?

Korea has over three thousand islands, so it helps to start with the easy, rewarding ones. Jeju is the obvious headliner, a volcanic island with Hallasan, lava tubes, beaches, and a completely different vibe, and cheap flights from Gimpo make it doable even for a weekend. Closer to Seoul, Nami Island near Chuncheon is a quick day trip famous for its tree-lined paths.

On the south coast, Geoje and the Hallyeohaesang area near Tongyeong are stunning, with a cable car and island-hopping ferries. Ulleungdo, far out in the East Sea, is dramatic and far less touristy, but it takes a few hours by ferry from Pohang or Gangneung, so save it for a longer trip. Near Incheon, Muuido and Yeongjongdo are super accessible for a half-day escape, and the Incheon ferry terminal connects to lots of smaller West Sea islands. For quiet and hiking, Hongdo and Heuksando off the southwest coast are beautiful. If you are just starting out, I would do Nami or a Muuido day trip first, then plan Jeju or Tongyeong as a proper weekend once you have the ferry and booking rhythm down. Book ferries ahead in summer and always check the weather, since rough seas cancel sailings.