So my wife and I will have a 15 hr layover at ICN in March.

We are flying in OZ from Sydney to ICN then onto JFK. We land in ICN around 7pm and dont leave till the next morning at 10am.

What can we do in that time to get the most out of it? I doubt we will need much sleep.

Also I dont know how luggage will be handled. Do we have to get it or will it just sit there overnight?

My guess is that it should be checked all the way through unless you ask them not to.

That is a long layover. Getting into the city is pretty simple so I would probably do that for a while. Seoul is a "city that never sleeps". But it sort of depends on what you like to do. I just spent a week and there were some interesting things to photograph at night which is something I enjoy. Depending when in March you are there it might be pretty chilly. In early April it was quite cool at night. Seoul has a very good tourism website so you can check that out to see what there is to do.

If it was me I would want a room to relax in. But I also like my sleep. There's a Hyatt right by the airport that I think you can get back and forth from on a maglev train. But staying in the city is also easy enough. You'd just need to be up early enough to get a train around 7 to get back to the airport.

Some neighborhoods that are active at night would be Gangnam, especially around Gangnam station. Hongdae and Itaewon are also lively at night. All of them will have some good places to eat and good hotels nearby. All of them will also have airport limo bus stops in the area.

For food, the area between Nonhyeon station exit #2 and Shinnonhyeon station exit #3, there is an alley parallel to the main street that has a bunch of restaurants that stay open late. This is in the Gangnam area.

You will have plenty of time to sleep on your flight to NYC so maximize your layover in Seoul and enjoy it.

Does Asiana still offer stopover hotels? I know Korean Air gives a hotel for paid tickets where an overnight layover is required (no earlier flight possible on the same day).

Nme has excellent ideas. If you stay near Sinnonhyeon there are many hotels and you can use Line 9 Express to traverse the city quickly.

We used United miles to book this ticket.