Mhar's Fossa

Mhar's Fossa is a gargantuan tunnel located at the end of a furrow that descends from Kadath, near the extremity of the Plateau of Leng. It was created when the Great Old One Mhar attempted to take advantage of the Storval Thinning, where the veil between Leng and Varisia is thin, to bore into the Material Plane before being trapped. Mhar's Fossa is filled with side branches leading to vaults and demiplanes. Nobody has dared exploring to its end, for fear that Mhar is still waiting.