Miles and miles of dirt roads up in the Sam Houston National Forest. Some minor hills, and some turns. You can even do some road work on Hwy 149, 1791, etc... If you want something even more challenging try Fire Road 9 off of 1791
If you do choose to ride up there be very careful. Lots of bikes, motorcycles, and a few cars on the hwy. Still good riding, but watch yourself and others.