However, there was an amazingly subtle reference early in the opening chapter. I've tried looking for references to it online and have not yet found anyone who noticed the connection (although, certainly, someone has). In short, Sapkowski (the author) is directly referencing the earliest Arthurian story that mentions the Holy Grail in the first chapter of his book. In it, the tower that a main character comes across appears and disappears much like the Fisher King's castle in the Chretien de Troye's Perceval, the Story of the Grail.
More importantly, towards the end of one of that first chapter's sections, a knight asks the character "What does the spear with the bloody blade mean? Why does the King with the lanced thigh suffer and what does it mean? What is the meaning of the maiden in white carrying a grail, a silver bowl--?" before getting cut off. These questions have no relevance to the Witcher story (so far) but are the questions that plague scholars of Arthurian legends who have read Chretien de Troyes' original story. In fact in that story, Perceval is later reprimanded by a woman (who turns out to be his sister) for not asking these questions. Thus, it was even more amusing to me when the character in the Witcher books asks the knight why he asked those questions--because the knight responds, "Well, to put it briefly ... One of our number failed to ask when he had the chance. He grew tongue-tied or was embarrassed ... He didn't ask and because of that there was great unpleasantness. So now we always ask. Just in case."
Some of you might know the meme with Leonardo DiCaprio pointing at something (a television) off frame. That was my general response to reading that section. I may have let out a single bark of laughter at the "So now we always ask. Just in case."
So we are clear, that is multiple layers of nerd showing there.