Taking into account all existing laboratory experiments, everything we know (i.e. lower bounds on parameters) about Dark Matter comes from cosmology and astrophysics, from phenomena that manifest themselves on proper-distance scales varying from 10^3 to 10^5 lightyears. I will first introduce the relevant concepts of basic cosmology, aiming at accessibility for non-cosmologists. Next, I discuss the relation between general-relativistic perturbation theory and newtonian simulations, and why this is a topic at all. Then I will show how state-of-the-art simulations can shed light on Dark Matter properties, if they can. Finally, I conclude with pointing out how these state-of-the-art simulations are off by several percent. There may be some pretty pictures of cosmological simulations.