Skull Mountain is a cave located just west of the Deep Dark Wood located in Skull Mountain - North. It is accessible by sea and air.
The first time Oliver is directed here is after he has acquired the incomplete Mornstar. To complete this much needed wand, Oliver must first find the three gems (magic stones) that complete the wand. To do this he needs a map which is under the watchful care of Kublai, leader of the Sky Pirates. As with most pirates, his residence has to do with skulls and bones... hence Skull Mountain.