https://youtu.be/wiO-Pxpskd8
The Tilly Foster Mine, in Brewster, NY was the deepest and largest mine in the world when it shut down in 1897, at 725' deep. Along with the deep open pit, miner carved out "drifts" or tunnels that went hundreds of feet into solid granite. The north wall tunnel system, which was discovered by our team in the spring of '15 has been fully explored and lines run. I believe these tunnels were carved out during there apex of operation between the 1860's-1870's, we are the first to see them since flooded in over 100 years.