The Line is a strange dimension. It appears as a giant snow-covered road, with mountains of "plowed" snow on each side. On both sides of these mountains are seemingly endless oceans of ice. The Line isn't always straight, and does tend to split into multiple trails. The Line is also prone to dangerous blizzards.
No one seems to know the origin of the Line, but things do tend to end up trap here. Often violent alien races. Because of this The Line can be considered a war zone, with skirmishes happening all across it between it's many inhabitants.
The Line itself appears as road in winter that was just plowed recently. The two "walls" on both of it's sides also look like the snow that plowed off it. The Line seems to be endless, and what's outside the line is most likely endless ice as well.