Neutrinos are “ghost-like” elementary particles that can literally go through walls. They can bring information from places that are impossible to observe through other means. This talk provides a glimpse behind the scenes of a next-generation neutrino detector called Hyper-Kamiokande – a cylindrical water tank the size of a high-rise building. I will describe some of the problems you encounter when planning a subterranean detector of this size, and explain how this detector helps us figure out why the sun shines and how giant stars explode.