The Forbidden Plateau was a high plateau lying beside a glacier in the Wu Pi Te Shao Mountains of the Yehimal, in the Utter East of southeast Faerûn. It was the site of the Kingdom of Nix.
The only way to reach it was through the elusive Phantom Pass, but even then, Nix only appeared once a year, around harvest-time. Vanesci Hamlet, a human settlement, lay near the entrance in Konigheim, many miles from Nix.
The almost-alien landscape around Nix was covered in slabs of gray stone and greenish swamps dotted with ponds. The trees were weirdly formed, with tendril-like branches and above-ground roots.