During gold-rush days the Argo Gold Mine & Mill processed more than $100 million worth of the precious metal. To transport the ore from mines in Central City, workers dug through solid rock to construct a tunnel to Central City, 4½ miles away. When completed in 1910 the Argo Tunnel was the longest in the world. During a tour of the mine and mill, guides explain how this monumental engineering feat was accomplished. Admission includes the small museum and a gold-panning lesson.