We have long wanted to go to a Sake Factory. This is more of a museum than a factory tour. Its a worthwhile activity while you are in Aizuwakamatsu.
The building is quite old and still in operation. There is an exhibit of how sake is/was made. Also you can walk through part of the actual factory. At the end and start of the route you can try and buy lots of their sake.
More photos from Aizuwakamatsu
Japan Tourist also has an excellent site with info about this area.