There are many planes of existence; some are far away, and others are closer. Some, like the Shadowfell and the Feywild are so close to the material world that they mirror it and at times even touch it. There is, however, another plane, though scholars debate whether it can truly be classified as a plane. Wizards call it the Morpheum, and Rho’vaani scholars call it Tel’Aran’Rhiod, the Hidden World. Others call it simply the Dreaming, or the World of Dreams.
Due to their unique backgrounds, all Kalashtar have the ability to enter Tel’Aran’Rhiod at will, though it takes effort to do so, and is extremely dangerous. While the soul explores the Hidden World, the body is sleeping and helpless; moreover, the Dreaming is home to many dangers unique to itself. Nightmares are very real there, and they, along with other, more benign dreams, can suck an unwary wanderer into them.