First time Costa Rica
 

That sounds like a great trip to me, short, but you're going to some good spots. We've stayed at both of those and enjoyed them. Right at the Arenal Observatory Lodge they have an observation deck where you can see beautiful birds and coatis. They put fresh fruit out in the mornings so it's best to go early a.m. We've seen oropendolas, honeycreepers, tanagers, etc. there. Also toucans in the trees near the restaurant and down by the spa. They do a free guided hike every morning if it's not too far for your husband to walk. We've seen howler monkeys on the grounds, and there are usually lots of coatis around. The Bogarin Trail is another favorite - easy flat trails owned by a local family who act as guides. We saw beautiful red-eyed tree frogs, poison dart frogs, birds, and several sloths there. Definitely do the guided option if you go. We would have walked by several things without our guide. It's located in town near the Catholic church. AOL has a shuttle you can take into town for about eight bucks per person if you don't want to drive. Cano Negro is excellent for seeing wildlife near the river - lots of caimans, water birds, and we've seen monkeys each time we've done it. It's a motorized, covered boat so pretty comfortable, and you can get fairly close to the wildlife. If a safari float interests you, Penas Blancas is fun; you float down the river in a rubber raft - have seen a croc, monkeys, and some nice birds when we've done it. Desafio is a good company for tours. You can explore their website and see what interests you. Don't forget a night at the natural hot springs; we like Tabacon or Eco Termales.

Sure, happy to help, j. Some of the boat tours have you walk down a sloping hill or go down steps to get to the boat so you may want to ask about that. Hope you have a great time.