The Hadeshorn sits at the center of the bowl of the Valley of Shale. It is a broad, opaque, and strangely still lake with dark, black water. Its flat surface glimmers with some inner radiance as if something pulses within its depths. Most of the time the waters are still, flat, and reflective, like glass.
The Hadeshorn is home to the shades of Druids, particularly powerful ones and ones who have served as Ard Rhys. Druids who have reached the end of their life go to the Hadeshorn, where they are carried away and down into the lake by the shades.
The waters of the Hadeshorn are anathema to life; touching the waters will cause death. However, the waters can be a source of magic. The Druid Allanon had Rone Leah dip the blade of the Sword of Leah into the waters of the Hadeshorn, changing its color to a deep black and infusing it with the magic of the lake. Allanon then sealed the magic into the sword using his Druid fire, creating a weapon that could cut through magic.