My knowledge is based on a Fodor’s book and having spent a week there. From reading, it seems most of the whitewater opportunities are in the Central Valley (around San Jose). La Fortuna is a base for many other types of adventure tourism (zip lines, etc) although we only did a rainforest hike that included hanging bridges. Also, we descended to the waterfall (Las Cateratas de La Fortuna), which was nothing short of spectacular and lovely—go midday and you can swim and sun for a few hours. If you are going to do a horseback ride to Monteverde do not take one over land from La Fortuna. It’s too dangerous. Instead take the Jeep-Boat-Jeep across the lake and replace the last Jeep leg with a horseback ride along the lake. I forget the name of the outfitter, but they’re in the Fodor’s book. If you’re going to Manuel Antonio, the book recommends picking up a snorkeling guide on the beach (unless you decide to go with an outfitter). The park there also provides plenty of hiking and swimming (at Manuel Antonio beach). You can hire a naturist guide (they hang out outside the park) or just sort of tag along loosely with any other guided group if you’re satisfied with spotting the wildlife without too much naturalist explanation about habitat, etc. I also don’t know exactly when the turtle hatching begins, but that would be a worthwhile activity if it works with your itinerary.