Rapoport--Zink spaces associated with unitary groups play a central role in arithmetic geometry. In this talk, I will introduce two types of unitary Rapoport--Zink spaces: one arising from global Shimura varieties and another with a simpler local structure. I will then explain how these two spaces are related. This talk is based on my joint work with A. Mihatsch and Z. Zhang, as well as some forthcoming results of my own.