Boyce Luther Gulley decided to put his mark on Phoenix, Arizona with a house for his daughter, Mary Lou. Mystery Castle was built in the 1930s near South Mountain Park. Gulley had tuberculosis so he had to move to Seattle, Washington, but he commissioned the home from any materials he could find, especially those that were inexpensive. Mary Lou and her mother did not know about the house until Gulley's death. In 1945 they moved into the house.
It was built with a combination of goat milk, cement, calcium, and mortar. There are 18 rooms in the three stories. Stone, automobile parts, adobe, rail tracks, telephone poles and other items were used in the construction as well. There is a chapel, dungeon, and cantina as part of the castle. Several areas of the Mystery Castle remain unfinished, and plumbing and electric were not added until 1992.
Mary Lou Gulley still lives in the Mystery Castle, though she does not lead the tours. She is often present during the tours, somewhere in the house. She opened up the house for tours for a few reasons. One was the eccentricity of the home, and the other is due to costs of upkeep.