The last site I visited in Gongju was Gongsanseong, which had originally been the fortress protecting ancient Baekje’s capital, Ungjin.
Gosanseong had originally been a fortress made of rammed earth, like Busosanseong.
The Joseon government built a stone wall in place of mere rammed earth, and the fortress which is there today is basically a renovated Joseon fortress.
In the year 1624, a rebel army took over Seoul, forcing King Injo to flee to Gongju, and of course the best place to defend himself was from inside the fortress. Supposedly, he took refuge at the very pavilion shown in the photo below.
While I was there, part of the fortress was closed for renovation. One of the parts under renovation is a dock for Joseon-era leisure boats. I could still see it from afar.
The best part of Gongsanseong, of course, is being able to take a stroll around the wall and see the pleasant scenery during nice weather.