The Legend of Korra – Book 2: Spirits
“Book 2 takes place six months after the first twelve episodes. It will focus on the mystical ‘Spirit World’ and the history of the Avatar lineage and mythology.
Unhappy and angry spirits begin to surface in the physical world. As the link between the two realms, Korra must not only keep the physical world safe from unearthly interlopers, but she must also learn what has provoked the spirits and restore balance between the spirit world and the physical world.”
From what I heard half of Book 2 will take place in Republic City and the other half will take place in other areas of the world. And two episodes will focus on Wan (voiced by Steven Yeun from The Walking Dead), the bender who becomes the first Avatar as a result of his attempts to balance the human and spirit worlds.
Season 2 of The Legend of Korra will premiere on Nickelodeon sometime in September 2013.