Our Pick
Posted on @rawstates
Cornwall Iron Furnace, still standing whole
1742
Cornwall, Pennsylvania
Wherring at en.wikipedia · CC BY-SA 3.0 · Wikimedia Commons
A charcoal cold-blast furnace that ran on ore from an open hill of magnetite next door, cast cannon and shot for the Continental Army, and kept working until 1883, by which time coke and anthracite had made it obsolete everywhere else. It survives complete with its blast machinery and stack, the only one of its kind left intact in the Western Hemisphere.
That was 1 of the hidden places.
Location: documented spot
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