You know a lot of the researchers here and just named dropped half the top 10 universities. I'll guess those are the ones with the partical physics departments. I don't know anyone here in that community, but I do know people who studied at all those universities.
I took a few Korean and professional cerificatiom classes at a few different universities but none of those. I live near SKKU Suwon campus, it's a natural science campus, so maybe they do particle research.
I haven't left the country since 2019, but tried once for a business trip and got turned back at the airport.
Fall is usually the best season to visit.
The particle physics community is indeed not that big so that it is definitely spread over only a few universities (especially theorists). I have checked what researchers at SKKU do (see here), and there is definitely a small overlap with what I do. However, it is sufficiently apart so that there is no surprise I don't know people working there.
I am looking forward to come back to Korea. For now, a lot of my Korean colleagues will probably all come to Lyon in France in June. I will let you know when I will travel Eastbound (the only condition is the no-quarantine one which is making it impossible to manage).