Neutrinos are among the most peculiar elementary particles we know. Their elusive quantum nature has always challenged scientists: they only interact with matter via the weak force, which makes them really hard to observe.To make it possible, scientists devised ingenious experiments and collected data for decades from rare interactions. But the more they observed them, the more neutrinos challenged our entire understanding of the universe. The most puzzling question is how neutrinos get their mass: its answer may hold the key to our understanding of dark matter and high-energy phenomena in the deep cosmos.