I love 19th/20th century factories, and my favorites are (of course) breweries. The Denver campus of the University of Colorado (Auraria Campus) sports a wonderfully renovated 19th century Tivoli brewery as its student union. It is worth a self guided tour (they have the old copper kettle and other equipment displayed) if you are in Denver for the GABF. It is about a 6 block walk southwest of the convention center.