The Harris Woolen Mill Ruins are preserved limestone remains of a small 19th-century woollen mill near Rockwood. The mill operated from the 1880s into the 1930s, replacing an earlier wooden mill that had burned down.
Most of the structure was destroyed by arson in 1967, but the stone walls still give a clear sense of the old industrial site. It is best treated as a short historic stop while exploring Rockwood Conservation Area rather than a standalone trip from Guelph.