Starry Night Over the Pontar is a painting by van Rogh, and an item in The Witcher 3: Wild Hunt added by the Hearts of Stone expansion. It may be acquired at the auction during the quest Open Sesame!, either for 20 or 60 crowns. If you gained the necessary information from Yaromir by correctly answering his question, buying the painting would later start the Avid Collector quest in which the painting can be sold on to Marcus T.K. Hodgson, a famed Novigrad book dealer, who will pay quite a tidy sum for it.