Life, Relocation
Zhalsuth launches his training with the Book of the Leviathan. Using his knowledge of the old world, he travels far and wide, collecting many powerful magic items. He also sets up a base of operations inside of the corpse of the Great Leviathan.
Zhalsuth does this largely to get back to his old power level but by the end he far exceeds it. With his newfound Warlock powers, he makes short work of any and all obstacles. Another observation he makes is that he no longer ages, even passed the end date of his second lifetime. His reasoning for setting up inside the Leviathan's previous form is simple: if another extinction event were to occur, he'd be most protected there. All of this is to work towards his new goal: bring the Leviathan back to the material plane. Only then it might be possible to bring back his old empire. Note: he builds his base in the image of Elryn's throne room.