I've walked the roughly 550-kilometer-long Gukto Jongju route from Seoul to Busan, but now I'm interested in the much-longer path (about 720 km) that follows the peninsula's east coast: the Donghae-an Jajeongeo-gil, or East Sea Coastal Bike Path, named for the Donghae, or East Sea (call it "the Sea of Japan" at your peril!). Even if you can't read Korean, you might find this site, with its lovely photos of that path, interesting.* A commenter recently informed me that the path, which previously didn't go all the way south, is now done, and it stretches all the way down to Busan. I had seen several contradictory maps showing both complete and incomplete versions of the path. Now I'm curious as to what's out there.
The problem, though, is that I'd need more than a calendar month to walk this path, and there's no guarantee that I can take off that much time. I could do the old "break the path up into segments" thing, but that would feel like cheating: walk the whole way in one go, or don't do it at all, I say. We'll see: there may be a way to wangle vacation time for this. (It might involve getting back into university teaching again!)
*A note about the above-linked site: you'll see it describes the path as being only 200-some kilometers long, with the 720-km distance being tagged with a gongsa-jung ("under construction") note. This information dates back to 2015, so it's not up to date.