Alcatraz was America's premier maximum-security prison from 1934 to 1963.
It has quite an interesting history, including the Native American occupation from November 1969
to June 1971 by 89 Native Americans.
Some interesting facts about the prison can be seen here: http://www.alcatrazhistory.com/factsnfig.htm
And here's a link to info about the Native American occupation: https://en.wikipedia.org/wiki/Occupation_of_Alcatraz
Very much worth a tour if you are ever in the area!