I visited Fujian Tulou in 2005, when there was only limited road access for tourists.  It is important to note that these villages are defensive in nature for the Hakka people.  The Hakka people migrated from north central China to flee wars in Henan Province in four major waves from the 7th to the 9th Century, and are resettled chiefly in four southern provinces, Fujian, Guangdong, Hunan and Sichuan.  Hakka in their language means Guest People.  As outsiders, they were subject to persecution and attacks, hence the circular shaped building where all activities are enclosed in the middle.  Homes are attached, with the defensive wall facing the outside.  The ground floor is for livestock, second floor for living and third floor sometimes used for storage.  There is a Hakka Museum in one of the buildings, giving a history of the Hakka people, including many prominent people in history, including political leaders of various stripes.  Included are the rebel leader Hong Xioquan (God's Chinese Son), who lead the civil war from c. 1840-60 that killed 30-40 million people, Mao, Deng, Singapore founder Lee, etc.

Interesting anecdote from the Cold War.  The US satellites took pictures of the Tulou back in the 60's and the Pentagon thought they were missile silos.