The two most important sites in this serial property are the Tomb of King Muyeong and Mireuksa Temple. The famous tomb, which was discovered intact, became one of Korea's most famous archeological discoveries. The tomb included items from Southeast Asia, China, and Japan. The interior of the tomb can only be visited by an onsite replica. Like Kaesong and Gyeongju, this WHS is made up of mostly tombs, fortresses, and temples. The fortress in Gongju and Buyeo are both pleasant walks, but have been partially rebuilt in later historical periods. I am very interested in visiting the Naesong City Wall, which (to my knowledge) was never rebuilt following the Three Kingdoms period.
While Gongju and Buyeo are very easy to visit, it gets more complicated in Iksan. First and foremost if you visit Iksan hopefully it's by car, as these sites are spread out and only few of them are accessible by bus. I visited Mireuksa temple site, and the Wanggung-ri Palace site. These historic areas really feel like archeological sites. There are few remains, but fascinating nonetheless. Interestingly enough the famous and enormous Mireuksa 5-story pagoda (originally 7-story) no longer exists in a sense. Pretty much the only major remain at the site, Mireuksa pagoda has been dismantled to strengthen the base and back portion. So what you see is a huge building over a largely disappeared pagoda. The original stones are numbered and laid out over an area the size of a basketball court, all properly numbered and waiting to be put back together. (Very much like a jigsaw puzzle) The pagoda was in serious danger of collapsing under its huge weight, so I think the current plan is the best option. Mureuksaji was likely the largest temple in Korea, and the pagoda is the largest. The Japanese in 1915 built concrete supports at the back of the pagoda, helping the pagoda last another hundred years. When the pagoda is put back together it will be whole for the first time in about 400 years. The pagoda dates back to around 600 AD, likely the oldest stone pagoda in Korea.
The Wanggung-ri palace site is almost completely gone with only another stone pagoda (5-stories high), and some small stone pillars, foundations, and wall structures remaining. (Much of the site is closed for archeological studies) In the Iksan area alone there have been more than 19,000 Baekje artifacts already unearthed. The sites in Iksan are interesting, but most visitors will come away somewhat disappointed if you don't also visit Gongju or Buyeo. I would recommend visiting some of the excellent museums to add value to the sites. Baekje mostly demonstrates its OUV because of its connections and how it came into contact frequently with Japan and China along its coastal areas though trade and regional dominance. (Noteworthy is Baekje's influence on ancient Japanese kingdoms) I am happy to see the Baekje Historic Areas become Korea's 12th world heritage site. In so doing, it completes the representation of Korea's many dynasties on the list.