There doesn't seem to be much information about what that facility is in Korea. According to ChatGPT, "independent researchers" have translated various map labels to "Anyang Aviation Radio Beacon." The "best" conventional explanation is it is an aircraft navigation aid, developed in the 50s. Wikipedia has an article about this tech
https://en.wikipedia.org/wiki/VHF_omnidirectional_range I'm not going to bother with all the technical stuff, but it usually deals with circular formation and an antennae. The thing in Korea, being on the side of a cliff, may just be built with a stone wall as support.
This is about the only ground level photo I can find, assuming it's the actual location. Can't really see the antennae. Apologies if any of these pictures are really large

Here is one in Oregon,

and one in Germany

Here is a similar structure in California, though it looks much newer