One of the distress messages in the bottle found in the whale's mouth is from someone who is was thrown into the dungeon by the wicked Horned King, fearing that evil will rule the world in "The Black Cauldron".
When Larry and Patti land in Sierra studios, one of the prop items they see is the black cauldron. When looking it, the game comments "That old tub dates from a very early Al Lowe game!".