Cauchy horizons are rather unique and peculiar objects that have been studied for decades. In this talk I will first review old and new breakthroughs on the subject by Isenberg and Moncrief, and by Petersen and Rácz, and then discuss joint recent work together with I. Bustamante where it is proved that non-degenerate Compact Cauchy horizons on smooth vacuum spacetimes (shortly CHs) have indeed constant non-zero temperature. It then follows by the work of Petersen and Petersen-Rácz that CHs are Killing horizons, and by the work of Beig-Chruściel-Schoen that such objects are non-generic on the initial data, (in agreement with the Cosmic Censorship conjecture). A null-orbital and topological classification of CHs will also be commented.