Weddingbicycling in South Korea - advices?

Hello. My boyfriend and I are going to marry, and for our honeymoon we are going to fly with our bikes for 3 weeks to south korea (in october).
so are there any advices (places, routes, festivals, curious things to do/see,....) ?? we just know about the 4 river cyclingpath and to cycle around Jeju, so please help us out with some other things.

thanks a lot