The gravitational wave instruments LIGO and Virgo have been transforming our understanding of neutron stars and stellar-mass black holes. Some mysteries have been solved, new ones have emerged. Upcoming LIGO-Virgo observing runs, the future operation of next generation ground-based instruments, as well as other observational means - e.g. pulsar timing arrays and the space-based gravitational wave observatory LISA - will continue to broaden the variety of astrophysical systems we observe: from billion solar mass black holes to sub-solar mass white dwarfs. I will discuss the implications of some of the most recent observations and future opportunities to study in detail compact objects over ten orders of magnitude in mass, and hopefully discover some hidden gems.