Map of South Korea. South Korea. South Korea is on the southern part—roughly one half of—the Korean peninsula, which juts off from the main body of Asia into the Pacific Ocean, plus islands off its southern tip. Its only land border is 238 km it shares with North Korea, which is the most heavily fortified border in the world. South Korea has water borders on three sides—the Yellow Sea to the west, the Korea strait, separating South Korea from Japan, on the southeast, and the Sea of Japan to the east and northeast.