The walls of Kaesong tell you what a medieval capital thought about safety. Goryeo's rulers lived behind several rings, an inner enclosure around the palace, a middle wall and an outer wall of earth and stone running around the hills for kilometres. The outer wall was begun in the early eleventh century, partly in response to Khitan invasions from the north, and was rebuilt and extended later. Parts are still visible along the ridge lines, with gates at key points, and they are now part of the World Heritage listing of historic monuments and sites in Kaesong, inscribed in 2013.
You will not find a road sign for them. Kaesong is in North Korea, close to the border, and the city is only open to foreign visitors on controlled tours with guides. If you are ever in a position to visit, the main landmarks are the palace site at Manwoldae, the old Confucian academy, the royal tombs in the hills and the bridge where Jeong Mong-ju died.
What interests historians is the idea of Kaesong as a trading capital. The dynasty traded with Song China and with Arab merchants, and the name Korea is said to come from Goryeo as foreigners first heard it. The city grew rich on ginseng, celadon pottery and printing. Goryeo produced some of the finest celadon ever made, with a delicate blue-green glaze, and the world's first movable metal type was probably used in Korea during this age.
The surrounding landscape is wooded hills and rice fields, with the long Songak mountain looming over the city. The climate has four distinct seasons, with a hot, humid summer, a brilliant autumn and a cold, dry winter.
For fuel and food in practice, a tour looks after everything for you. Meals tend to be long, ceremonial affairs, and the local cooking is regarded as among the best in Korea. If you want a sense of the place without crossing the border, museums in Seoul hold excellent Goryeo celadon. Treat this entry as a story, not a route.