24-Hour Layover in Seoul

Hi,

I have a 24-hour layover in Seoul as part of a larger trip, and would like to make the most of it. This would be my first time in Seoul.

Realistically, I will only have time to see your city at night (not too late) and in the morning.

With this in mind, I would please like your suggestions as to what is a must see, where to eat/visit, and what area of the city should I be looking to book my hotel at?

Thank you in advance.