The "Black Light" is the counterpart of the "White Light", where one can convert to the evil Goddess [[Libila]]. To reach it, head North West from the "[[White Light]]", which can be seen from the whole of wurm.
NOTE - If you join Libila you automatically become [[Horde of the Summoned ]] aka 'Blacklighter (short: bl'er)' (HOTS) and cannot spawn or go anywhere near NT.