Thunder Rift

Campaign world for TSR's "Challenger" series of introductory Dungeons & Dragons adventures, accessories and novels. Thunder Rift was created as a standalone campaign that could be slotted into any fantasy world. But the intention of the designer, Colin McComb, was always that it was part of Mystara, somewhere in the mountains bordering Karameikos (source). This beginners' campaign was then designed to lead players to the more complex world of Mystara, and the adventure Escape from Thunder Rift provided this link explicitly.

Thunder Rift is a self-contained valley surrounded on all sides by sheer cliffs nearly half a mile high. There are only a few known exits out of the valley to the rest of the known world. There are very few settlements surrounded by a vast wilderness for players to explore. Hordes of Goblins, Kobolds and Orcs roam the various hills. A band of bandits have a hidden base somewhere in the north of the valley.