If you want an amazing WWRR experience and are flying into or out of San Jose, check out the Rio Pacuare...the best WWRR I've ever done and it's so beautiful!
La Fortuna the list of things to do is so long it's hard to name them all but here is an idea of the things you can do here:
LAKE ARENAL: fishing, kayaking, bird watching, wake boarding, sunset boat cruise, party boat cruise...
LA FORTUNA/VOLCANO ARENAL: Hiking in one of the many parks (Reserva Silencio de Mirador, National Park, 1968), Try a different Ziplining Co like EcoGlide or Aventura (that goes over the Rio Fortuna waterfall) although know that SkyTrek is still the best in this area, Proyecto Asis Wildlife Rescue, Ecocenter Danaus, ATV, horseback ride, Rio Salto (where the locals go to swim in the river and there's a rope swing-just ask around), hot springs (too many to choose from, each with their pros/cons), rappel down waterfalls-I like Pure Trek's the best, and much, much more!