The last novel in Andrei Sapkowski's Witcher saga, The Lady of the Lake, draws heavily from the Arthurian legend, from its obvious title, to the naming of characters like Nimue and the Fisher King, over Ciri ending up in Arthurian Britain and meeting Sir Galahad,
to Geralt's and Yennefer's mythical "death" and travel to (what is similar to) the island of Avalon...
What I do wonder, though, is if that is only so prevalent in this very last book of the series or if the earlier novels already employed references to the Arthurian legend that I simply missed. As a (possibly hard to answer) related question in the former case, I'd also like to know if Sapkowski always planned to reference the Arthurian legend at the end since the novel series' inception or if he decided that rather on the fly when writing the last book.