Took a trip up there recently and was blown away by the designs of this place.
Built around the 1100-1400 AD by the Sinagua people. This 5 story and 20 room castle built in a cave was used for shelter. Ironically the name of the place isn’t even related to the people who lived in it. The name was actually given back in 1867 the early settlers who believed that it was Aztecs.
The castle itself is about 90 ft high and built inside of a cave in the Camp Verde area of Arizona. Access through the castle was through ladders that were probably raised or lowered through trap doors in the ceiling to prevent enemy advances or access. One of the main reasons the Sinagua chose to build the Castle so far above the ground was to escape the threat of natural disaster in the form of the annual flooding of Beaver Creek. At the time water pretty frequent in those areas and during Monsoon season, the creeks would build up and flood the nearby areas.
The dwellings and the surrounding area were declared a U.S. National Monument on December 8, 1906 as a result of the American Antiquities Act, signed  earlier that year. It is one of the four original sites designated National Monuments by President Theodore Roosevelt. Montezuma Castle was added to the National Register of Historic Places on October 15, 1966
Links are posted below for anyone who would like to read more.