Google "Texas State Parks." Most are small, but pretty, and the weather in Texas means that it's almost never a bad time to go outside. Closer to Dallas try Mineral Wells, Deactur Grasslands, and Eagle Mountain Lake. For day shit try the Trinity River trail system for good bike paths. The Brazos River has a lot of canoeing and kayaking potential. Farther trips: Palo Duro Canyon, the "mountains" in Eastern Oklahoma, Government Canyon, Colorado Bend, Big Bend Ranch/National Park, Padre Island National Seashore, Pedernales Falls, Garner State Park, eastern Texas has piney woods. Also floating the river is really popular, there's a music venue in Fort Worth that operates in the summer and you just hang out in a tube while a band plays and get drunk, the rivers down in the Hill Country are awesome because of all the natural springs. There's several private campgrounds and swimming holes around springs too and a lot of real pretty waterfalls in the Hill Country.
