Although neutrinos are among the most abundant particles in the Universe, they are also among the most mysterious: they are neutral, very light and only weakly interacting, and therefore can traverse the entire Earth, the Sun and even galaxies. This makes already just the detection of these tiny particles an exciting research challenge. But there is a lot more to neutrinos: Since the discovery of the electron neutrino in 1956, three different species of neutrinos have been observed, with hints for the existence of even more so-called neutrino flavors. It has not yet been possible to determine the absolute masses of neutrinos, nor their mass ordering. Another open question is the symmetry or asymmetry of the behavior of neutrinos and anti-neutrinos, which might help us understand the imbalance of matter and antimatter in our Universe. All these mysteries have the potential to uncover physics beyond the standard model of particle physics and neutrinos could be the key to a new understanding of the subatomic world.