We've done both the very physical (whitewater rafting) and totally laidback tours in Costa Rica. The latter was a tour of a pineapple farm/plantation and processing plant. If you're looking for excitement this isn't it, but it was VERY informative and we did really enjoy it as it gave us more insight to another side of Costa Rica.
We have heard that others have taken "tropical garden" tours and have very much enjoyed those as well. I understand that those tours are usually a solid one hour bus trip each way.
We have also just "winged it" and hired a driver to take us around Limon and the surrounding area and had a great time! We saw a small private aviary at a home on the ocean just outside Limon, stopped for a snack at El Faro Restaurante which is at the highest point in Limon and has a great view of the city and the coastline, and also stopped at public beach (can't remember the name right now) that had some nice views and crashing waves. Whatever you do you can't go too wrong in Costa Rica. We've been there 3 times - can you tell we love it there? :grin