PattiS,
DuPlooy's has a marvelous botanical garden on site. Just ask and they will arrange for a nature tour around the facility. We loved it! So many flowers and plants and trees!!! All were so lovely. I think your parents would definately enjoy this. As I mentioned before, duPlooy's is right on the Macal River but it is a VERY steep trek down a narrow, winding, stone pathway to the water. Going down wasn't so bad, but coming up may pose a problem. If your parents enjoy bird watching, the resort sends large trays of fruit out into the canopy every morning, by pully, to attact the numerous birds, which include tucans and parrots. Bring binoculars!!! San Ignacio is a short ride, and the management can arrange a trip into town for a lunch outing or shopping. Surely, there are many points of interest in town. As Lan mentioned, there are a few day trips that I think your parents could handle. I believe duPlooy's has most of their tours listed on the net. Print it out, and see what your parents think. BUT... The management there is fantastic, and don't feel that you are only limited to those tours. They would be happy to arrange anything for you.
Debbie