Nanjing Part 1

Nanjing is a six hour fast train ride from Guangzhou (with quite a few stops). It would probably be at least a three hour drive from Shanghai.

Still probably not on the western tourist route but somewhere I wanted to visit for its history some of which is not especially savoury. There is a really good article here on the Wikipedia.

First the unsavoury part. In 1937 the Japanese (detailed account Wikipedia) invaded Nanjing as the then Capital of China as part of the second Sino-Japanese.

" The massacre occurred over a period of six weeks starting on December 13, 1937, the day that the Japanese captured Nanjing. During this period, soldiers of the Imperial Japanese Army murdered Chinese civilians and disarmed combatants who numbered an estimated 40,000 to over 300,000,^[7][8] and perpetrated widespread rape and looting.

Since most Japanese military records on the killings were kept secret or destroyed shortly after the surrender of Japan in 1945, historians have been unable to accurately estimate the death toll of the massacre. The International Military Tribunal for the Far East in Tokyo estimated in 1946 that over 200,000 Chinese were killed in the incident. China's official estimate is more than 300,000 dead based on the evaluation of the Nanjing War Crimes Tribunal in 1947." 

Perhaps the most scary part is that this episode is completely absent from history teaching in Japanese schools. 

There is a very large, informative and tasteful memorial museum recording this event.

I found the whole museum / memorial really moving and for the most part quiet and treated with respect and silence by locals - the exception being the occasional tour group rushing through the place chattering away at the tops of their voices.