Hong-do (6km long by 2.5km wide) is one of the most beautiful - and popular - islands in Dadohae Haesang National Park. Nicknamed the Red Island, it has a wealth of extremely unusual rock formations, which can only be properly observed from the boat that goes around the island. With the exception of the villages and the small Ppadol Beach covered with quartzite pebbles, Hong-do is protected and for the most part walking here is prohibited.