Many believe Skull Island to be a mythical place, but it does exist. One of the reasons for it being considered legendary is that map makers often put it in the wrong place or exaggerate its size.
Skull Island is found in the Barrier Ocean, generally west of Brinston and the Slyvanian Forest. Despite maps to the contrary, it is only generally shaped like a skull (sort of an upside down pear) though it does have four smaller islands south of it that fanciful map makers have deemed to form into crossbones. It is a rough place with boulder strewn edges, and the only plant life is found as the hills rise in the central region. The island is roughly 36 miles across (west to east) and 54 miles north to south. The shoreline is dangerous to boats of all kinds with all manner of underwater obstacles. Though many are natural, some have been added by various inhabitants.
The most notable resident in recent memory was the wizard Phosforensiatic, the villain of the Battle of Brinston. It is assumed that he is the cause of the many undead that still can be found on the island. Most people assume that he controls the island still, but those who are more in the know believe that he was assassinated by Stolin the Deadly, an assassin paid by the government of Brinston (one of Jasper’s first acts) to eliminate the threat and prevent a future scenario that may have proved more successful. Here again, opinions vary as to whether or not Stolin accomplished the task. Some believe that Phos escaped, while other believe that he has since become undead as a means to circumvent just this sort of attack. In any case, Stolin was a believer in humans being the destined race and was planning attacks on the various nobles of the Slyvanian Forest. Therefore Stolin was either killed or chased out of his new base on Skull Island by a team of adventurers sponsored by the elves. Some believe that a new inhabitant, known as the Ruby Mage, has taken up residency, though other believe that he moved on to the Great Archipelago instead.
Even assuming that none of the previously mentioned (extremely powerful) villains is currently in power or based on Skull Island, it is still an extremely dangerous place. Just in the last 30 years, it has been populated by countless undead (though most of them mindless) and riddled with traps. Its natural environment is also deadly in that there are frequent avalanches and rare fresh water or food sources.