riverrat

To start with, you are heading to the most beautiful river in Texas. It is sparkling clean but it does run low. We have "walked" the Frio a time or two. Garner can be crowded so if seclusion is what you are aiming far, you may miss the mark. 30 or so miles to the northeast is Lost Maples Natural Area. Great hiking and fewer people but no real swimming except at the Ponds. 30 minutes or so south of Garner is Neal's Lodge at Concan. Great smimming hole but not much free parking and usually lots of people.
Anywho...back to Garner...hiking there is good. Be sure you have a map and know how to read it and trail signs. It is easy to get on the wrong trail at a couple of spots but you can always find your way if you keep Old Baldy in sight. Our fav is to go up to White Cave and go left at the old rock fence then around to the downside of Baldy. This is very steep going up and then again down but fairly level the rest of the way. Carry LOTS of water. There is none on the trails. A good bit of shade can be found on all of the trails. As far as geocaching goes, I have no clue but it would probably be a great place for it.
They have picnic tables at the day use area near the swimmming beach but if you want one, get there early to claim it! Remember, the squirrels love oreos!
Have a great time!