The Ice Run was a network of ice-walled pathways stretching all along the face of the Great Glacier. These twisted and winded, making a quite tortuous maze. All in all, they extended several hundred miles in length.
Many of these paths were open to the sky, but the sun above reflected off the walls of ice, filling the passages with dazzling light. This could be quite bewildering to explorers, and so the open tops offered no better chance of escape.
The folk of the White Worm tribe saw the Ice Run as their holy ground, and also used it as a defensive retreat. Only they knew how to traverse this hazardous maze, and they most often wandered there. This most unwelcoming of tribes was especially hostile to trespassers.
The Ice Run was naturally very dangerous for explorers.