Alex and I spent a ton of time walking this trail. It's a local favorite and you can also rent kayaks, canoes, and paddleboards of off the lake nearby.
Zilker Park is great for a picnic day, but there's also a lot more to explore nearby. The botanical garden, rose garden, and the Umlauf Sculpture Garden are all worth checking out, and the sculpture garden is especially cool.
Another iconic place in Austin! Great for a hot day, but the water is freezing so beware!