Although technically not abandoned, it probably will not be long before it is.
A 40 foot imperial style lighthouse built in 1833, it is the oldest working lighthouse on Lake Ontario, now that Toronto's Gibralter Point lighthouse is no longer operating. It was manually operated until 1978, and the fog horn was silenced in 1991. The light keepers cottages were sold, and it now sits on private property.
Treat yourself to a $5 round trip ferry ride on the 3-car cable ferry to Simcoe Island, and follow the Nine Mile Point road, pretty much the only road on the island.