AFAIK there aren't any arrivals lounges at ICN, although you might be able to use a PP lounge after the flight if the security setup doesn't prevent you from getting to the door. Similarly, I'm not aware of showers in any lounge at ICN, but I haven't checked since the new terminal was opened.

KE used to send some passengers (elites in business class and IFC?) to the spa/health club (at the indoor pool in the old tower) of the Grand Hyatt ICN.