Costambar is a very small, mainly residential area, just to the West of Puerto Plata. I will try to describe it - please bear in mind, though, that it is now 13 months ago since I visited. Something could have happened or changed since.
Everything is quiet, safe and peaceful. It is cleaner than a lot of places in the DR. You will mainly - but not only - find fairly well to do Dominicans and quite a few ex-pats in Costambar. There is a school, a taxi station, a nine hole golf course (aptly names Los Mangos) and about a dozen restaurants. We enjoyed the Italian one greatly as well as the Dominican one just by the gate to Costambar (yes, there is a gate to the whole community).
Shopping? Not much. You will find a grocery store or two in the village and a super market right by the gate. Enough for everyday items but for bigger shopping you will have to go to Puerto Plata. This doesn't take much more than ten minutes by gua-gua (shared taxi) or taxi, so it isn't a problem.
Inside Costambar you can walk everywhere. I have heard people (only Americans - are you guys trying to replace your legs with tires?;-))complain about distances, but from one end to the other it is hardly more than a mile and we never found it strenous although we had two small children along.
The beach is long, wide and sheltered, fringed with sea grape, mango trees and almond trees. Most places there is coral in the water so bring sandals or look out! The beach in the next community West of Costambar - which is named Cofresi - is better for swimming. You can walk there in about twenty minutes if you follow the shore, but you will have to cross a river. It isn't deep but you can't help getting wet. It's fun and the view on the way is lovely. If you don't feel like this, simply take a taxi. In Cofresi you will find another good selection of restaurants and bars as well as a few souvenir shops.
All in all Costambar is very enjoyable and although there are some tourists (a few apartments, a good B&B named Villas Olas Tropicales, some villas, a small all inclusive etc.) it is very relaxed and closer to everyday life than a lot of other places.
Depending on how long you are staying I would consider going for a trip to Samana for two or three days. You can take the bus from Puerto Plata. It is fast, cheap and comfortable. It leaves in the morning. Samana is another world altogether. You can find more about it on www.samana.net (link below).
Enjoy your stay there.
Regards,
Susanne