Caverns of Fear is a Masters of the Universe read-along book by Mary Carey with artwork by Al McWilliams, published in 1983 by Golden Books.
While riding Battle Cat near Castle Grayskull, He-Man stops to get his companion a drink from a nearby well. While Battle Cat drinks, He-Man hears the sounds of swords ringing against each other and climbs down to investigate. He discovers a network of caverns at the bottom of the well, and is suddenly attacked by Mer-Man. He-Man manages to knock him out and enters the caverns, reasoning Skeletor can't be far away.
His suspicions prove true: not far ahead he finds Teela locked in combat with Skeletor. She had seen him entering the caverns in order to find a secret entrance into Castle Grayskull. Beast Man attacks then but is knocked into a pit by He-Man, who then turns his attention on Skeletor. Trap Jaw shows himself and takes Teela captive, but Man-At-Arms and Stratos then enter the fray. Man-at-Arms smashes Trap Jaw's mechanical arm with his mace while Stratos carries Teela to safety. Outnumbered, Skeletor uses magic to teleport away.
He-Man batters the cavern walls with his sword to cause a cave-in and block the entrance to Castle Grayskull. He-Man learns that the reason Man-at-Arms and Startos came to his rescue is that when he didn't return, Battle Cat went looking for help, and praises the tiger's worth. The Heroic Warriors go their separate ways.