Talk:Lionhead Spider Cultists' lair/@comment-207.6.82.252-20151220111958/@comment-2604:2D80:402D:891C:12C:226:4AE8:F6A9-20171011115952

In addition to what I posted before about the quest page, another page regarding the letter itself has an interesting note. They think that judging by the way the letter is handled by the mechanics this might have originally been intended as a fully functional quest but was not completed. So, possibly something that didn't survive development but they didn't see the need to remove it either, left it as an Easter egg.

http://witcher.wikia.com/wiki/Letter_for_Knight_Eric