There is a park entrance fee. Be careful at high water times/seasons.
This is a super-accessible trail that takes you right along some of the most scenic parts of the entire Guadalupe River.
The sculpted rocks and natural sitting/swimming pools are accessible in low water times...shaded by the beautiful cypress trees that line the trail. If you are in the area, it's very much worth the park entrance fee (5 or 10 dollars).
If you want a more natural trail experience, you can run the singletrack right along the river's edge, which runs parallel to the paved trail.