With the prefix WG6, which means it’s a World of Greyhawk module, it’s another adventure taken directly from Gary Gygax’s game as he explains in the foreword. Interestingly it’s a part of the Greyhawk campaign that was never actually played as the original players decided not to go there.

It’s always frustrating when a DM sets up an interesting place for players to go and they refuse to do it. The advantage of having your own TTRPG company is that you can then publish that place in a module and sell it, so it wasn’t a complete loss. The story as you can imagine from the cover is a straight take on the King Kong and Skull Island story, you get caught in a demiplane in an island where there’s a big ape and you need to take your high level party to sort stuff out. 

This is, as is usual with Gygax adventures aimed at high levels, a bit of a meatgrinder, the island is full of powerful monsters which can easily make your characters into paste and a bunch of spells (particularly those dealing with nature and animals) do not work on this demi-plane. Gygax also designed this to be used with Unearthed Arcana, so you need that book to play this. If you are a fan of King Kong, take your players through this and may god rest their souls.