Welcome to Below and Beyond Kyvid.
For the past fifty years, the borders of the Atlos Desert have continued to creep forward. Nobody has discovered the source of this expansion, but this is not the first time this has happened. The Atlos Desert was not always a desert, but thousand of years ago it was a fertile land desired by many. Why the land is now desert has been the topic of many debates, but archeological digs have revealed more then one ancient city that was thought to be a myth beneath its surface.
The PCs have all been drawn to a strange location in the deep desert where a massive sandworm had been pinned beneath the surface. The sandworms body had served as a tunnel into a strange location filled with alien monsters, symbols, and architecture. Many of the creatures within its halls were twisted forms of humanoids and goblinoids, brought to this location and warped by the touch of the Far Realm.
As the introduction drew to an end, the players discovered that the Goddess Ioun had been traveling the desert to discover the source of the expanding and corrupting sands. He search brought her to this very location where she was attacked and dragged into the Far Realm by an unknown entity. The PCs knew that the world changed on this day and the times to come will be harsh indeed. Not all hope is lost though, as the PCs have been asked by an angel of the Ioun to seek answers to what happened this day.