The most common mistake on a first 2-night, 3-day Jeju trip is covering east and west in one day. Jeju is about 73 km east to west and the loop is over 200 km, so an ambitious plan leaves you in the car for 6+ hours. Split it into one east day and one west day.
Day 1 — East
Pick up a rental car at the airport, then Hamdeok Beach, Manjanggul, and Seongsan Ilchulbong, about 3 hours of driving. Manjanggul is a UNESCO lava tube at 11 to 21 degrees inside, so bring a layer, and add Udo (a 15-minute ferry from Seongsan) if you arrive early.
Day 2 — West
Hallasan Eoseungsaengak or Saryeoni Forest, Hyeopjae and Geumneung beaches, and an Aewol sunset, about 3.5 hours. Day two is the real full day.
Day 3 — City and airport
Keep it light near the airport with Dodubong, Iho Tewoo, and Dongmun Market. Staying around Seongsan and Pyoseon keeps day-two travel manageable.
See full day-by-day routes and driving times