We survey recent developments on collapsed n-manifolds with (lower) bounded Ricci curvature. Compared with those non-collapsed manifolds or collapsed manifolds with bounded sectional curvature, obstructions of collapsing under lower bounded Ricci curvature hardly are known. Examples were constructed recently, illustrating that those collapsed Ricci limit spaces are far away from a manifold. Around 2016 Rong proposed a program to study collapsing under an additionial assumption, local bounded covering geometry, which aims to find necessary and sufficient conditions for the existence of nilpotent structures in the sense of Cheeger-Fukaya-Gromov on collapsed n-manifolds with lower bounded Ricci curvature. We prove several main conjectures on the main goal of this topic, and extend Fukaya's singular fibration to the case of bounded Ricci curvature and local covering geometry. These are two joint works, one with Liang Cheng and Yongjia Zhang, and another with Cuifang Si.