Halaster's Lost Apprentice
Halaster Blackcloak created Undermountain long before most of what is now Waterdeep was built. Undermountain is supposedly filled with deadly traps-mechanical as well as magical-andalso a horde of bizarre creatures crafted from Halaster’s sorcery. Most accounts settled on Undermountain spanning nine levels and fourteen sublevels, but no one knows what the influence of the Spellplague might have worked upon it.
The top level of Undermountain is home to the shift community of Downshadow, an underworld for the capable but temporarily impoverished—in other words, other adventurers. Folk of Downshadow are known throughout Waterdeep as dangerous and untrustworthy.
Recently, some hidden chambers of Undermountain within Downshadow has been discovered. Of the explorers who found the entrance to the Hidden Chambers, only one returned alive. He claims that the way is open, though only brave adventurers have any chance of sruvival. Anyone who kept a wizard’s sanctum hidden for at least a century’s worth of nosy adventurers must have used powerful magicks to ward it. If it’s been discovered now, it means the magicks are waning, and it’s a good chance to explore the Hidden Chambers.
An eladrin swordmage called Xeres has publicly declared ownership of the Hidden Chambers, and vowed that anyone who attempts to explore it will be punished.