Mystery Castle in Phoenix, Arizona, is easily the most bizarre building I’ve ever toured. 

“It was built in the 1930s by Boyce Luther Gulley (died 1945) for his daughter Mary Lou Gulley. After learning he had tuberculosis, Gulley moved from Seattle, Washington, to the Phoenix area and began building the house from found or inexpensive materials. Boyce Gulley died in 1945, and Mary Lou and her mother were notified by attorney that they had inherited the property. Shortly after, the mother and daughter moved in.  Said to be held together by a combination of mortar, cement, calcium, and goat milk, the sprawling 18-room, three story castle is built from a wide range of materials—stone, adobe, automobile parts, salvaged rail tracks from a mine, telephone poles, etc. It features a chapel, cantina, and a dungeon.”  (text from official wiki - a nice article on the structure with more photos — fun fact I got to meet Mary Lou when I toured her home)