Great Park
I think this is one of my more favorite parks I've camped at in Texas. The rock is quite something to behold and it is one of the darker sky areas in central Texas. There is still plenty of light pollution from the nearby towns but you can see many stars. If you are adventurous see if you can find the "caves" at the top of the rock.
Pros: Pretty and cool during the fall/winter. Great trails, "splunking" available, nice campgrounds.
Cons: Small, there are not a LOT of trails, but if you are only hiking there is plenty still.
SitePrimitive Campgrounds
Month of VisitDecember