A little-known fact among many Americans, South Korea is actually quite mountainous. In fact the highest mountain in Seoul is Bukhansan. Playing children and hiking grandmothers (ajemas) will fly past you while you stand captivated by the view of one of Asia's megacities. Insiders tip: This mountain is easily accessible by Seoul Metro's Line 6. The best time for a hike in Korea is in the fall, preferably in October when the foliage is turning and the weather is warm with just a tinge of cool in the air.