I agree with andymo99. The KE FC lounge at ICN is the best I have ever experienced. I have been in the lounge many times and have never seen it even approach crowded. I haven't tried to get in since they banished ST Elite Pluses, but I did go into the Presitge Class lounge once just to look around and, while its not as nice as the FC lounge, it was still head and shoulders above any US airline club.

It's easy to find. It's in the center of the terminal above the KE departure level transit desk. After your arrival, you'll ascend to the second (departure) level. Once there, follow the signs to the airport transit hotel. That will take you up an escalator. At the top, you'll have a restaurant/lounge/game room on one side and directly opposite are the KE lounges.

Depending on how long your layover is, the transit hotel is a decent option if you don't want to go out of airport. They rent the rooms in 6-hour time blocks and the rooms, while certainly not plush, are great for relaxing. It's operated by the Sheraton Walker Hill, but alas, no SPG credit!