From PathfinderWiki

Viperwall is the name of the notorious keep built on the eastern shores of Ember Lake in central Varisia.1 Its many conical towers and serpent carvings emit a sickening green light and poisonous fumes, so it is to no surprise that the place is greatly avoided by the local population.234 Rumor has it that the castle was built sometime in the mid-fifth millennium AR by serpentfolk who traveled up from Sekamina through the Mobhad Leigh in order to create a surface outpost for their race. Others believe that the fortress has existed since the time of Thassilon.5 Deep within the keep is a portal to the ruins of Sverenagati.6

Recent history

The parents of Zimandi Kaddren, head of the prestigious Kaddren family of Magnimar, recently disappeared while exploring Viperwall.7