I visited this WHS in April 2017. I only visited the sites in Ganghwa Island closest to Seoul but after a number of video documentaries (the best one for an overview is https://m.youtube.com/watch?v=6osPwzl5OIE) and from information from the Ganghwa History Museum I visited (just opposite the dolmen park in Ganghwa), I would only visit the other sites if I were passing by the area as their only difference is the sheer amount scattered on the hill sides.

First of all let me explain how I got to the Ganghwa Dolmen Park and the other minor sites on Ganghwa island. By subway I got to Sinchon "Bus Terminal" (Exit 4). From there my suggestion would be to forget the misleading title "Bus Terminal" and without crossing the road simply look for the first lamp post with a bright red sticker showing Bus 3000. That is where you'll have to wait for the 90-minutes bus ride to the main town of Ganghwa-eup. A printscreen with the name in Korean and a picture will help the bus driver know where you want to go.

Once you get on the island from Ganghwa-eup Bus Station, head to the small tourist information booth and ask for information to the Bugeun-ri Dolmen Site (20 minute bus ride). The friendly staff will write down the bus number for you as well as the platform number and departure time. Once you get to the largest dolmen in Korea you can follow a 2km hiking trail to the minor Jeomgol Dolmen, and further on to Chunguk Samgeori but this one is not on the UNESCO list. One bus stop before arriving to Bugeun-ri (free entrance by the way!), you can hike to the Osang-ri dolmens but you won't get anything better than the large one in the dolmen park (photo). The UNESCO inscription certificate plaque is just in front of it too. The dolmen is lit up and accessible at night if you happen to have a rental car and be in the area. The Ganghwa History Museum (closed on Mondays) is worth visiting mostly for the few remains and the informative models illustrating the most plausible methods of how the dolmens were built.

Having visited quite a number of prehistoric sites myself, I wasn't impressed by this WHS as there are no temple structures or apparent alignments (like in Carnac for example). The large dolmen is very similar to the one in The Burren in Ireland and so I failed to appreciate its OUV. Nonetheless, I'm glad I visited by public transport as a taxi ride would have cost me an arm and a leg!