Incheon Airport opened in 2001, replacing Gimpo (Kimpo) Airport, now serving domestic sites. ICN has a golf course (I actually saw golfers out in the sub-zero weather), a museum, spa, casino, transit hotel and a mass transit link with Gimpo and Seoul. A nine story hospital is being built to serve the airport and surrounding area. There are 74 gates, but expansion is already proceeding to have 128 gates by 2020. It is already Airbus 380 (up to 840 passengers) capable. Seventy airlines fly into ICN.
I spent some time in the Asiana Lounge.