My prime reason for going to Phnom Penn is that it is the base for the Tabitha charity. The city used to be the cultural heart of not just Cambodia but the whole of Indo-China. It's prime 'attractions' are to do with the holocaust of the 1970's in the Tol Suleng genocide museum and the killing fields. However the city does host the Royal Palace and generally a nice laid-back vibe.
Phnom Penn (ភ្នំពេញ)