A Calabi-Yau manifold is a Ricci-flat Kahler manifold. It is a longstanding question to understand how the Ricci-flat metrics develop singularities when the complex structure degenerates. An especially intriguing phenomenon is that these metrics can collapse to lower dimensions and exhibit very non-algebraic features, and it is challenging to describe the corresponding geometric behavior. In this talk I will discuss an answer to this question for a special class of degenerations. Based on joint works with H. Hein-J. Viaclovsky-R. Zhang 2018 and with R. Zhang 2019.