What do you think about these activities: We'll be at Playa Naco from Dec 14-21
Outback Jungle Safari
Amber Museum
Mount Isabel de Torres
Brugal Rum Factory
The Malecon
Fort San Felipe
outback jungle safari: fun but expensive, as it has been pointed out. the only thing is that travelling alone in rented jeep you will not get info into plantations to see cocoa, coffee and other exotic stuff (but i was curious about it, you may not be). check what does safari offer, sometimes they have a horseback ride (horses are very calm, more like ponies, so if you LIKE horse-riding better don't do it), and they always include lunch. best if you have some friends here who can drive you through the countryside.
amber museum: never been
mount isabel: i like it, good place for picnic and views are stunning! one of my favourite places in POP.
brugal factory: very noisy, it's like being in discovery channel "how it's made". you can buy lots of memorabilia, good gifts for those back home.
malecon: nothing to be seen, really. nice walk thou. ocean on one side, dominican architecture on the other.
san felipe: i never made it during opening hours, gotta work...
my advice is a cemetery, very weired.