Home of Making in the Mournland. Travel here with Karshak from Eston.
The Glass Plateau is mostly smooth and flat, though jagged spikes and spires jut up from the ground in seemingly random places. The central portion of the highland plain is obsidian, and bursts of fiery light can sometimes be seen in its dark depths. Toward the edges of the plateau, the glass becomes lighter in color and more transparent, appearing almost pale white along the jagged cliffs at the edge. Nothing grows on the plain of glass, and few creatures haunt its jagged peaks and flat expanse.
https://www.dndbeyond.com/sources/erftlw/building-eberron-adventures-the-last-war#TheMournland