If you are in Jaco, Costa Rica and have the time I would suggest an ATV tour. Jaco is on the Pacific side of Costa Rica about in the center of the coast. I tried several different tour operators. All offered a great tour with each one taking you on different terrain.
The tours I went on started in Jaco and headed inland. Some go high into the mountains and one stayed on mostly flat terrain but crossed several streams. Most end up at a waterfall and believe me, by the time you get there you are ready to jump into the pool at the bottom of the falls. I enjoyed every tour I went on.
One of the unexpected sites was as you head inland you pass many small villages that I had no idea were there. Some of the villages had a bull fighting arena. The roads back there are a combination of paved and dirt roads with mud holes, rivers and jungle.
You can book any length of tour but I would suggest either the three of four hour tour. They both give you time at the waterfall to relax in the water before heading back. The mountain tour ends up at a small outdoor cafe for food and drinks and they also have a tarzan swing if you want to try that. The flatter tour with more river crossings has several bars in the villages where you can stop and get a beer.
Since you will have a lot of tour operators to choose from I would look around and pick the right one for you. You don't have to go far. Along the main street are many places to get information. Also, I've talked to families that also took their teenage children and they had a blast.
One thing to note, you are crossing rivers and going through mud holes. Wear clothes and shoes you don't mind getting dirty. The tours are also very dusty. I would bring a bandanna. You can also buy one from the tour operator. You'll need it.
Bring water and a camera and enjoy.
I plan on going again when I am in Jaco in January 2015.