Sun:
If you are going to the beaches in the Pacific, then keep in mind that during the Christmas week through New Years, the beaches get super crowded due to locals from San Jose going for a week to the beaches. Great beaches to see are in Guanacaste: Playa Flamingo, Tamarindo, Jaco, Playa Hermosa. Great points of interest are: Arenal Volcano & Hot Springs, Monteverde Cloud Forest, Rincon De La Vieja Volcano. They offer zip lines, hiking, swimming, tubing and horseback riding among other things. These locations are several hours from the beaches.
Suggest getting a book on CR to map out your trip.
Regards
Lou