ICN is a breeze. There's actual sleep rooms that are quiet, have dim lights and have full length recliners that you can sleep on (as a bonus there's partitions between the recliners so you get some privacy). If you want something better, Walker Hill has hotels inside terminal 1 and 2 where you can get an interior room (no windows) with a bed, bathroom, etc. It's a little pricey but you can get it in 12hr increments.