Sometimes you need to spend your time in the airport after midnight. It can be due to multiple flights schedule or late time arrival and there's no public transportation. Whatever it is, it's very useful for you to know what is 24 hr facilities in the airport before you fly off. 

FYI, I upload some good information about 24 hr facilities in Incheon International Airport. 

24 hr food

24 hr coat keeping

24 hr internet zone

24 hr Spa

24 hr Relax Zone

Transit Hotel (in the airport)

I knew that Incheon International Airport is big, but I never expected it's huge like this. As they have lots of great facilities, I think it'e better for you to check what kind of places and facilities they have inside, if your flight is arrived at Incheon International Airport.