In Goseong, a seaside town only seven miles south of the 38th parallel that divides the Korean peninsula, stand three houses, where the triumvirate of postwar Korea—Kim Il-sung, Syngman Rhee, and Lee Ki-poong—once vacationed in the summer. In a still-unified but Japanese-occupied Korea, Goseong was a resort town for missionaries. In 1938, one missionary named Sherwood Hall commissioned a house on a bluff overlooking the shores of Hwajinpo Beach to a German architect who had fled Hitler’s reign. The result was a three-story villa, crenelated like a medieval castle and…