Best 10 Day Split
A strong Korea first trip is four nights in Seoul, two nights in Busan, and three nights in Jeju, with one buffer night depending on flights. Seoul gives palaces, markets, shopping, cafes, and nightlife. Busan adds beaches, seafood, temples, and coastal scenery. Jeju gives volcanic landscapes, waterfalls, coast roads, and a very different pace.
Seoul First
Seoul is large, so plan by neighborhoods. Use one day for palaces and Bukchon, one for markets and shopping, one for Hongdae or Gangnam, and one for a flexible day trip or food focus. Choose accommodation near a subway line, not only by neighborhood reputation.
Busan by Train
The KTX makes Seoul to Busan simple. In Busan, choose whether you want beach access near Haeundae or city convenience near Seomyeon. Add Gamcheon Culture Village, Jagalchi Market, coastal walks, and Haedong Yonggungsa Temple if timing works.
Jeju Planning
Jeju is not as easy to do by casual public transport as Seoul or Busan. Rent a car, choose guided day tours, or plan accommodation around the areas you most want to see. Weather matters, so keep outdoor routes flexible and avoid booking every scenic stop back to back.