Ontario built its economy on manufacturing, mining, and resource processing. When those operations closed, they left behind buildings, machinery, and engineered landscapes that are now among the most compelling exploration sites in the province. The industrial ruins of Eastern Ontario have their own character (limestone mills along canals), but the province's industrial archaeology extends from the mine headframes of the Near North to the factory districts of Hamilton and the hydro-power infrastructure of Niagara.
Water-Powered Mills
Ontario's first industrial revolution was water-powered. Every river with a decent drop had mills — flour mills, sawmills, woolen mills, paper mills. The concentration along the Mississippi River through Almonte and Appleton is the best example: a string of substantial stone mill buildings that processed wool for export across the British Empire. But similar sites exist on the Rideau, the Tay (Perth), the Speed (Guelph), and dozens of smaller rivers.
What makes Ontario mill ruins interesting is the infrastructure around them. Mill races (engineered water channels), dam structures, tailrace outlets, and the supporting buildings (warehouses, worker housing, offices) create a complete industrial landscape rather than a single ruin. The best-preserved examples have all of these elements visible.
Mining Infrastructure
Northern Ontario's mining ruins are industrial archaeology on a different scale. Mine headframes (the steel towers over shaft openings) are the most visible features, but processing plants, tailings systems, rail infrastructure, and company-town buildings create complex sites. Cobalt has the highest density of mining ruins in the province, but the Sudbury Basin, Kirkland Lake, and Timmins areas all have significant sites.
A word of serious caution: mine sites are genuinely dangerous. Shafts can be hundreds of feet deep and not all are fenced. Tailings contain toxic materials. Processing plant buildings may have chemical contamination. Stay outside structures and away from shaft openings.
Railway Infrastructure
Abandoned railway infrastructure — roundhouses, coaling towers, water tanks, and yard facilities — represents another category of industrial ruin. The most significant remaining roundhouse ruins are scattered across the province, often in small towns that were once division points on main lines. Bridge abutments and trestle foundations along abandoned corridors are the most common and most durable railway ruins.
Hydro-Electric Infrastructure
Ontario's early electrification involved hundreds of small hydro-electric generating stations on rivers across the province. Many were decommissioned as the provincial grid consolidated onto larger stations. The physical infrastructure — dams, penstocks, powerhouse buildings, and transmission towers — often remains. The Ragged Chute compressed air plant near Cobalt, which used falling water to compress air for mine operations, is one of the most unusual industrial sites in the province.
Urban Industrial Districts
Ontario's cities all have former industrial districts in various states of conversion and abandonment. Hamilton's north-end steel district, Toronto's Port Lands, and Ottawa's LeBreton Flats are well-known examples of industrial landscapes being transformed. In smaller cities, industrial conversion is slower and more uneven, leaving buildings and infrastructure in a liminal state between abandonment and redevelopment.