McKinney Falls is located 15 miles from downtown Austin and is home to two waterfalls, ample spots for relaxation, and swimming in the summer months. Remember the $6 Entrance Fee (Free with a TX State Parks Pass).
McKinney Falls is separated into the Upper and Lower Falls along Onion Creek just 15 miles outside of Austin. The pin I dropped on the map gets you to the parking lot at the Upper Falls. From there it is a very short walk past the Smith Visitor Center to the falls. The upper falls offers some shady areas underneath beautiful cypress trees and an area to swim near the falls. It's not uncommon to see groups of local Austinites hanging out, swimming, drinking beers, reading, playing guitar and generally escaping the noise of the city for the day. It's also a dog friendly park, so many people will bring their furry companions.
To get to the Lower Falls you actually have to get back in your car and drive to it. While it's only about a mile down the road you'll have to follow the signs from the Upper Falls parking lot to find it. From the Lower Falls parking lot it's another very short walk to the falls. If you're wanting to just hang out at one spot for the day, my advice would be to scope out both spots and decide where the best option is to enjoy your day there. Sometimes one of the falls can be busier than the other. Either way you decide this is the perfect spot to get away for the day or weekend (there are a few primitive campsites available).