In practice going backwards is the only way to bicycle here, and is relatively safe. It's not strictly marked as one way either.

The sidewalk/cycle path does not exist here for about 200m, where there is only a shoulder. But going the wrong way on the shoulder is the only way to travel east here by bicycle. Presently routing will instead send cyclists in the main eastbound lane, which is very high speed and has no shoulder in some places.

Trail damaged by floods in 2018. I added it back, maybe incorrectly, but marked it as gravel and smoothness=bad. It can be passable.

There is no such thing as bicycle=yes in Korean law. Only designated and dismount.