Did you know Korea has developed a wonderful biking infrastructure along major rivers and coasts? They have convenience facilities (water, shade, bathrooms, even free compressed air). . . you can even buy a "bike passport" (with map) for W4000 and collect stamps. You get stickers for each completed route, and (very impressive! worth more than the W4000) medals and certificates when you complete all the major rivers or Incheon to Busan. There's an app (in Korean) if you want to track you progress that way or meet fellow riders. Lots of campgrounds and hotels along the way, too. I've stepped back from climbing a bit these past few years-- well, this is where I've been! Biking!
"If you can't do something well, you might as well learn to enjoy doing it poorly."
-- from a de-motivational poster, but I find it oddly liberating