What is dark matter, the mysterious predominant constituent of all matter in the Universe? While particle dark matter has eluded detection thus far, as I will demonstrate, large dark matter experiments themselves form impressive neutrino telescopes. This opens a new window into astronomy as well as major problems such as the origin of supermassive black holes. Drawing on lessons from neutrino astronomy, I will also show how signatures from transient sources could lead to new insights into the fundamental properties of axions. I will then demonstrate how intimate connections with astronomical puzzles as well as ongoing boom in gravitational wave and multi-messenger astronomy are particularly pronounced for primordial black holes from the early Universe that make an attractive non-particle dark matter candidate. In fact, primordial black holes from the general formation scenario of bubble multiverse might have already been seen by Subaru Hyper Suprime-Cam.