Big Thunder Gold Mine

Two German immigrant miners, W.B. Krupp and J.A. Engle, discovered this gold mine in 1892 — drawn separately to Keystone, South Dakota, connected by a common language, and eventually partners. Originally named Gold Hill Lode, the mine they drove into solid rock still stands in near-original condition. Today it operates as a working attraction, with guided underground tours and gold panning along Battle Creek. The adit cut through solid rock — not timbered, but self-supporting — is, the site notes, why it's still open to walk through.