Nice! You are somewhere around mile marker 100. If you are looking for a break 25 miles or so in, between mile 76 and 77 you will reach the Killiansburg cave on your left (pretty obvious, since on your right is water!) that is kind of a cool thing to see and there are a few info signs scattered around. A mile or two later on you'll see smaller caves, then reach Lock 38/Ferry Hill area which has lots of open porta-potties and many photo ops, too - but might be crowded on the 4th.
Enjoy the last day!