The nearest airport is in Seoul (ICN-Incheon Intl.), located 23.5 mi (37.8 km) from the city centre. If you're unable to find a flight that fits your schedule, you might consider flying into Seoul (GMP-Gimpo Intl.), which is 6 mi (9.6 km) away.
Catch a ride on the metro at Guil Station for ease of access to the rest of the city.