Almaden Quicksilver County Park sits on a former mining operation. Santa Clara County bought the mines in 1976, ended operations, and opened up the park for recreation. The mine itself was used to extract mercury found within cinnabar ore, and remnants of the operation can still be seen. In various parts of the park, you can find abandoned buildings, old mining equipment, collapsed mine shaft entrances, and even abandoned vehicles. The New Almaden Quicksilver Mining Museum is also nearby if you wish to learn more.
Parking is extremely plentiful (and free!), with an overflow lot that can probably accommodate a few hundred cars.