Castle Hill is an isolated pink granite monolith standing in the heart of the north Queensland city of Townsville. It rises to a height of some 286 metres above sea level and dominates the city skyline. It is one of the most distinctive natural features on the Queensland coast. There are a number of vantage points from which to view the city below and also across Cleveland Bay to nearby Magnetic Island.
The hill is an inselberg of Carboniferous-Permian origins, rising abruptly from the younger Quaternary coastal plain. The surface is primarily bare rock or shallow lithsols with small areas of duplex soils. There are three peaks to the summit. There is a former quarry site on the southern slopes, accessed via Stagpole Street, and on the northern cliff face a large graffiti on 'The Saint' is painted.