It's not going to be easy to get your car out of the campground, but if you really want to try...
Head out of the venue back toward Vantage. Take a left at the crossroad on the other side of the Vantage bridge and drive about 4 miles. You'll come to an old campground called Getty's Cove. Right next to it is a small bridge that you can park next to and either jump off it into the water or climb down the rocks. It's a bit of a drive to get there, but it's a really fantastic and refreshing place to swim.
Thanks for all the help! I am just looking at Google Maps to try and figure out exactly where this is. Is the left you make after going over Vantage Bridge called Huntzinger Road? And are Getty's Cove and the small bridge inside Wanapum State Park, or even further south?
Does anybody knwo of any good swimming holes near the venue? Given the talk about the long wait for dirty showers, taking a morning trip to a river/lake seems like a good option. Thanks in advance for any suggestions.