Shore up the defenses!
Fire and death! The oracles tell of portents in the clouds that give dire warning: great foes and enemy hordes approach Castle Grayskull (no relation)! The walls are at threat of collapse from enemy cannon fire, ballistae, and the newly discovered Black Powder Bombs. We require the aid of a Legendary Hero, or the support of a Great Army! However, we have nought Hero nor Army, and the castle's lord fears that his reign will be shortlived.
Will you defend Castle Grayskull (no relation)? Or will you let it fall? The fate of the lord and his keep rest in your hands!
The Underground
Deep within the halls of Castle Grayskull (no relation) lies a dungeon. Within this dungeon is a crazed old man, who tells tale of a Legendary Hero who will appear in a time of great need. You will know the hero of whom he speaks, when a young adventurer delves into the depths of the Labyrinth and finds the Legendary Weapon. He smiles and laughs, repeating the tale in a broken ecstasy, his voice echoing down the dank halls of the underground dungeon.
Perhaps the Hero is truly marked by a Weapon that is to be found? Something to save Castle Grayskull (no relation)? But where might it be found? And what labyrinth does the old man speak of...?