ICN is Incheon Airport near Seoul, South Korea.

Traveling back to Los Angeles from Bangkok, I had a 5 hour layover in ICN.
South Korea encourages travelers with long layovers to exit the airport for free trips to various spots near Seoul, which is about an hour from the airport. They provide free shuttles for shopping, temple tours, BMW factory, casino, etc.
All you have to do is sign up at the Free Transit Tour Desk (TTD) before going to through the Transit Inspection Checkpoint and show your through boarding pass. All tours include a guide except for the casino tour.

You can visit the casino without signing up at the TTD, but if you do, they will give you a voucher for 70,000 won (won is the currency of South Korea) free play, a free gift (key chain), and free cafe dining. Also the desk will give detailed instruction on how to exit the airport and catch the shuttle to and from the airport.
The casino is only 5 minutes by shuttle from Terminal 1, about 25 minutes from Terminal 2.
It runs every 20 minutes and is very easy to catch outside exit 14.

On arrival, you can check your bag/carry on at the desk and register for a players card, you must present your passport, as no South Korean citizens are allowed in the casino.

Then you go to the desk opposite the registration and get your key chain and register for your free play.
They will give you a 20,000 won free play TITO for the slot machines.
Upon entering the casino, you tap your card at the kiosk to get your 50,000 won voucher for a one bet table game voucher.
The voucher is printed below, in the drop drawer, not obvious from the kiosk until I asked at the players desk.

I played off the slot voucher in a 100 won per spin machine and won a total of 2000 won (about US1.50), for a 10% return.

Then I played the table game voucher at a 10,000 won minimum baccarat table and won on banker.
The table minimums range from 10,000 - 200,000 won.

I played a couple more hands and cashed out 36,000 won, score.
Chips used are 1000, 5000, 10000, and up.

Overall the casino is in a large space, but has very few slots and tables compared to Vegas or California Indian casinos.
No craps, just blackjack, baccarat (the two most popular games), 3 card poker and Sic Bo.
You can buy in chips with foreign cash at the tables at the current exchange rate and they will give you a receipt.
When you cash out, they will give you the same currency back up to the amount you buy in on the receipt, minus a transaction fee.
(I bought in US$100 at 123,000 won but cost me 128,000 to get $100 back)
If you win, the remainder is in Korean Won.

I spent a total of one and a half hour outside the airport. If you have at least 3-5 hours, its not a bad way to get free casino souvenirs.