Takachiho (高千穂) is known as the land of Japanese Mythology (日本神話). There are lots of shrines and places that are related to Mythology. And also Takachiho Gorge is one of the “Must-See” spot in southern Kyushu area.
Nichirin (にちりん) connects Beppu (別府) and Oita (大分) with Miyazaki (宮崎) and Miyazaki airport (宮崎空港). A few of Nichirin are extended to operate to Nakatsu (中津) and even Hakata (博多). Hyuga (ひゅうが) is an intercity train in Miyazaki prefecture. This train is operated on same route as Nichirin. But it is operated between Nobeoka (延岡) and Miyazaki airport. If you travel along the east coast of Kyushu, you may need to take these trains.