In Fiery Gizzard State Park, there's a recreational lake with swimming and picnicking facilities at the site of the historic Lone Rock Coke Ovens, where locally-mined coal was converted to coal coke by convict labor. An easy 2.3-mile hike encircles the lakes; some of it using a low-traffic paved road. Access this adventure from the Grundy Lakes Trailhead, which is also the parking area for the swimming and picnicking facilities.