Adder’s Heart: The Tower of Set in the Dust Desert connects to an ancient and vast tunnel complex that extends deep into the Underdark and to the large cavern network of Deep Raurin.
It was partially constructed by Keoth Amsetis (the godking Set) as he explored the even more ancient ruins of a far older complex created by a magically powerful group that predated even that of ancient Imaskar, gathering magical knowledge that would make him the most powerful magic user in the Raurin Empire (and later Mulhorand) and earn him the position of Fa Vizier (Grand Vizier).
It is unknown exactly when Set turned against the godkings of Mulhorand, or when the Tower of Set became home to the zealots that worshipped him, but it is likely that shortly after -1048 DR, when Set was exiled from Mulhorand, that the Setites moved into the Tower of Set and expanded the tunnel complex beneath it to become the Adder’s Heart.
Over the millennia the strength of the Cult of Set waxed and waned, Set was absent for long periods of time and the group often fell victim to political infighting, eventually around -50 DR he vanished and did not return.
By 922 DR and the time of rebellion of Thay, the Cult of Set was at its apex and used its power to exploit the chaos and weakness of Mulhorand, hoping to oust the godkings once and for all. Unfortunately, Mulhorand recovered quickly from its failure to defeat the rebellion and set about eradicating all presence of the Cult of Set, launching a terrible inquisition against the Setites and driving the few survivors underground.
Although the Tower of Set was never discovered, its inhabitants cut themselves off from all other cells and dispersed among the Raurin nomads or into the depths of Adder’s Heart, vanishing completely or becoming natives among the nomads of the Oasis of the White Palm.
Today the newly arisen Cult of Set, led by the Divine Incarnation Seti, has only just begun to explore the depths of Adder’s Heart, which has become the home of many monsters from the surrounding Deep Raurin.
Vuthivyr: The baetith that once used the Thaymount as a secret base to perform its secret magical research were attended by many lesser races, including various sauroid and humanoids. When the sarrukh empires fell and the baetith abandoned their outposts, the sauroids that served them were abandoned to their fates.
The settlement of Vuthivyr is one such group of sauroids that survived from the time of the sarrukh. This group of lizardmen and troglodytes) fled into the Underdark and came to Deep Raurin where they thrived in the lands below. They were regularly raided and enslaved by the Imaskari, as well as the illithids of Kallectoll, but survived beyond the fall of both those powers.
Today the Vuthivyr have grown powerful and in great numbers by stealing the magical legacies of the Imaskar and Raurin Empires. The magical energies from Raurin above have leached down into Deep Raurin and granted the sauroids of Vuthivyr enlarged size, intelligence, and unusual abilities, this coupled with the magic stolen from ruins of Imaskar make the Vuthivyr a force to be reckoned with.
The Vuthivyr are nomads, and they now avoid the land beneath the Plains of Purple Dust due to the purple worms living there. They mostly roam beneath the Dust Desert and the Desert of Desolation, emerging at night to raid the lands above in groups of fifty or more.