Information on domestic flights:
- Most flights to Jeju are from the Gimpo domestic airport in Seoul on Korean Air (the last flight from Gimpo to Jeju leaves at 9:05pm, and the last flight from Jeju to Gimpo leaves at 9:05pm), and costs around $200 USD for a roundtrip.
Korean air: www.koreanair.com.
Other airlines: can be found here.
- Most of you will likely be flying into Seoul Incheon Airport on your international flight and then taking a paid bus connecting to Gimpo Airport (it takes ~50 minutes) for your flight to Jeju (there are flight between Seoul and Jeju every 15 minutes, and it takes ~50 minutes each way), so please plan your trip accordingly.
For detailed info on how to get to Gimpo/Seoul airport from ICN airport, see:
https://indico.cern.ch/event/1133243/attachments/2427432/4156069/ICN_GMP_2.pdf