The Hiyode Mountains is a very hazardous mountain range, and is very difficult to cross. Even so some people have attempted it but most are turned back, and sadly a few are killed. The best way to traverse them is by airship. The Hiyode Cave is located at the summit of the tallest mountain. Though it is unknown what is inside because cimbing the tallest mountain is considered by many to be suicide. Some speculate that there are treasures in there that have yet to be found, other believe that it's just a cave of ice.