Originally Posted by KQ321

I agree it shouldn't be a problem. If you're non-Korean, you have to fill out an Immigration card, which will have a space for 'address' and/or 'purpose of visit' (I can't remember the details, but there's definitely something). However, if you put down 'transit', and explain to the official at passport control that you don't have an address because you're just going landside between flights, they should be fine with that. Same thing applies when you fill out the departure card, when going back airside later on.

Just one other thing to watch - the queues for (non-Korean) immigration at ICN can be pretty long at peak arrival times, so you may need to factor this into your planning. I don't recall such delays on departure, though.