If you have only a few hours' layover at Incheon airport, why not have a glimpse to North Korea through the border where is about 65km away from Incheon airport.  Based on our private tour service inclusive pick up & drop off at airport, you only need 4 hours to visit Odusan Unification Observatory  where is 460 meters to border line and the narrowest  Demilitarized Zone between South Korea and North Korea. If time allows, also visit Imjingak Peace Park where displays Freedom Bridge and Locomotive Train as relics from Korea War.
Alternatively, every Monday will change to visit other Observatory without Imjingak Peace Park.