La Fortuna is one of the best bases for white-water rafting in Costa Rica. The Balsa River, 20 minutes from town, offers Class II-III rapids — good for beginners and families — with jungle scenery and reliable wildlife sightings along the banks, including birds, monkeys, and basilisk lizards. The Toro River nearby runs Class III-IV and is better suited to those wanting more intensity.
The Pacuare River, a longer drive southeast, is the big one: two to three days of Class III-IV rafting through a remote canyon of primary rainforest, with camping on beaches between the rapids. Most La Fortuna operators run the Pacuare, either as a day trip from San José (a long day) or as an overnight expedition. The overnight version is worth the extra cost and planning — few experiences in Costa Rica match sleeping on the riverbank in a canyon where there is no road access and no other sound except the river.