As a visa exempt, "short term" entry with no alien residence card (aka not registered).....you ABSOLUTELY 1,000,000% must quarantine for 14 days at a government facility. This means they bus you to some hotel somewhere. Many say it's actually very nice, but of course everyone has different facilities and I wouldn't wanna find out haha. Of course they feed you 3 meals a day, too.

You must pay the fee yourself and the total cost is 1,400,000 KRW (around 1150 USD). You must have a phone with working mobile number (some people say they've had a hard time getting a SIM card/pocket WiFi) and install an app to self-monitor and enter results for the govt to check. They visit you periodically to make sure you're staying in the room (also the app has GPS tracking) and if you don't report in the app your temperature etc. twice a day.

This is for ANY foreigner entering Korea. Nationality doesn't make a difference.