Atop 367 miles of mine shafts tunneling almost a vertical mile beneath the surface, Gold Country’s best-preserved gold-quartz-mining operation is worth a solid half-day’s exploration. From 1850 to 1956 the miners here, mostly Cornish, produced 5.8 million ounces of gold (worth about $8 billion today). The visitor center has maps and leads guided tours (schedules vary).
It's very well worth paying to enter the mine yard, littered with mining equipment and buildings constructed from waste rock, and to view the main shaft's claustrophobic entry, next to the head frame (a tall structure used to haul ore and people from underground). Nearby is the English-manor-style cottage and rose garden of the Bourn family, who originally owned the mine; though this now appears incongruously idyllic, the noise of the mining activity must have been deafening.
Hiking the trails that meander past abandoned mines and equipment is free. Trailheads are located at the parking lots behind the visitor center and Penn Gate to its west.