Dekanter
More correctly, these are the Mines
of Dekanter, the only known accessible ruins of lost Netheril (the other known
ones are "in the Land of the Lich Lords" aka the "Fallen Lands").
In ancient days, the mines of Dekanter provided the realm with iron. As the mines
were worked out, Netherese mages used them for research, to isolate the effects
of new spells, and to store magical paraphernalia. When Netheril fell, all was
abandoned, and the mines became an extensive crumbling ruin surrounded by low
hills (talus piles from the mines). Above the hills, gaping holes and hidden entrances
open on the dark mysteries within. The magic that once filled Dekanter is long
depleted, and it now serves as home to goblins, gargoyles, and others. Goblins,
gnolls and gargoyles live in the mines, known minions of something described as
"the Beast Lord".