Phnom Penh, Cambodia
It seemed unthinkable to visit Cambodia and not devote some time in the capital learning about the horrors of the Khmer Rouge period of the 1970s, and so we spent several hours at both the S-21 Genocide Museum, and Killing Fields of Choeung Ek while in Phnom Penh.
These sites of course cannot be classfied as "enjoyable visits", but they both provided excellent audio commentaries and written information to supplement the experience. The S-21 site is actually a fo...