AREX and Subway Line 2 stop running around midnight. After that, please use the Airport Limousine Bus or a taxi.
Available at any convenience store (CU, GS25, 7-Eleven) inside the airport. Works on all subways and buses.
The Airport Limousine Bus is much easier β no stairs or transfers with bags.
Naver Map or KakaoMap (Google Maps is limited in Korea), Subway Korea.
Around 60,000β80,000 KRW + tolls. Takes about 1 hour without traffic.