The Old Windmill, Tower mill in Spring Hill, Brisbane, Australia

The Old Windmill is a four-storey tower of stone and brick built on a circular trench cut to bedrock, about 9 metres in circumference, on the highest point of Wickham Terrace. Two pairs of millstones inside were driven separately by sails and by an external treadmill. It is the centrepiece of Observatory Park.

Built in 1828 by convict labour, the tower mill ground wheat and corn for the Moreton Bay penal settlement, with a treadmill used when wind failed and as punishment; grinding ceased in 1845. From 1855 it served as a signal station relaying shipping news, and in 1861 a time ball was installed to regulate clocks and watches. It later hosted early radio, telephony and television research from the 1920s.

From 1855 the tower served as a signal station relaying shipping news between the Brisbane River mouth and the town, and in 1861 a time ball was installed so residents could set clocks and watches. A signalman's cottage was later built beside it, since demolished.

The tower stands in Observatory Park at 226 Wickham Terrace, Spring Hill, beside Wickham Park, on the highest point overlooking the settlement site. The park is open to walkers, and the tower is seen from outside; the observation platform and iron railings are not opened for public tours. The site is a short walk from the Brisbane central business district.

The structure held a darker role in colonial history as a place of punishment and forced labor for prisoners. Inmates operated treadmills while wearing heavy shackles, revealing the harsh conditions of the early penal settlement.