South Korea’s southern island of Jeju beckons with trek on a hidden trail through Geomunoreum, a UNESCO world natural heritage site. Geomunoreum International Trekking, an event taking place Thursday through Monday, will be held around Geomunoreum, a volcanic cone northeast of Hallasan, South Korea’s tallest mountain. The five-day event offers a rare opportunity to explore Yongam-gil, a restricted zone. Y.