Murney Martello Tower
This tower was constructed in 1846 as a part of the new naval defences authorized for Kingston Harbour by the Imperial government during the Oregon Crisis of 1845-46. It was one of the last British works of defence commenced in the Canadian interior and one of the most sophisticated of the Martello Towers built in British North America. Although in regular use as a barracks after 1849 it was not fully armed until 1862, when it had already become obsolete because of rapid advance in offensive military technology.
Plaque via Alan L. Brown's site Ontario Plaques. Full page here.