In the dark cave, like the arrival of darkness, this stronghold hidden underground was covered with a mysterious veil. This is not just a simple darkness, but the tunnel is covered with shadow elements. In this stronghold, a huge shadow-type magic array is shrouded in. Anyone who walks here will be unable to see his five fingers. Unless he has a special mark used to identify the magic array, only with the mark of the magic array can he walk naturally here.