Never Mountain is a rocky peak adjacent to Never Lake. Before RBR, the mountain was unremarkable. After his domination of Mobius, however, Doctor Robotnik had his face carved into it and tethered the Miracle Planet to it with a giant chain. Even after Robotnik's downfall, the chain remains attached to the mountain.
Never Mountain was not obvious during the events of The Brotherhood of Metallix, the chain appearing to just be attached to any mountainous part of Never Lake.