BAEKRYEONG — It is South Korea's westernmost territory, soldiers outnumber residents, and you can see North Korea from almost every barbed wire-lined beach: Welcome to Baekryeong Island, a community on the front line.

Far closer to the North Korean mainland than it is to the South, Baekryeong is a fortress: Tanks are parked at the sides of roads, there are guard posts on every hill, and the picturesque beaches are covered in dragon's teeth — concrete pyramid-shaped fortifications — to deter invasion.