If you are looking for a river adventure, Las Tinajas and Charco frío are your best bet. Located just 20min away from Las Gaviotas, you have a great time enjoying this beautiful hike.
We recommend that you take hiking water shoes for this. I found this website that is extremely informative and they offer tours as well. Please be sure to read all the information on this website, as Las Tinajas is a bit more offroad and not for everybody, but Charco Frío is more family friendly.
Make sure to take cash with you as the parking will need to be paid in cash, I believe is less than $10.00. We recommend at least $20.00 since there is no cellphone reception; Hence, no credit card transactions available.