Rockville Hills Park is a 600-acre park in Fairfield, California. Originally bought by the city to be made into a public golf course, Rockville Hills instead became an expansive public park. With a multitude of trails interwoven throughout the oak grasslands and volcanic rock outcroppings, this park has a great variety of trails and natural spaces for hikers and bikers.
After parking in the small lot, you will have an option of four different trails moving in all directions. Each route has unique rock structures, caves, small lakes, and even more offshoot trails. While in the park, make sure to visit the larger "Upper Lake," which often has a multitude of waterfowl and frogs along its banks. There are also many spots where you can do a bit of bouldering on the volcanic rocks that have been thrust up through the ground.
There are often events taking place in the park such as group mountain bike rides, ranger-led walks, and even haunted hikes for children in October.
Note that in places there are so many trails, many of which are simply signed as "unknown," that it can often be difficult to find your way back to the parking area. Make sure to carry a map or GPS so you can easily return to your starting point. Also, keep an eye out for the poison oak that is ubiquitous off trail.