The walls are usually crowded with people walking along them. That's why I tend to visit during winter or bad weather when it's less busy. I just got really lucky with the visibility that day, probably because it was a Sunday and right in the middle of COVID-19 so all the tourist programs were closed.
I wanted to try HYBH community and I like it. I'll give the app a close look soon, but I don't really like posting from my phone unless I have no choice (travelling without netbook). I pinned this location in my first blog about the larger fortifications and impressive buildings at the Northern End that I featured last fall. Suwon is actually worth visiting for tourists coming to Korea if they don't have time to get to somewhere far from Seoul because it's only a 40-minute train or bus ride and is an easy day trip.