Puerto Plata city is a Victorian-era port town that most resort visitors skip entirely — which is exactly why it's worth a half-day. The centre has genuine character: gingerbread wooden houses, a handsome central park with a gazebo, and a Malecón seafront promenade lined with restaurants and cafes. It feels like a real Dominican town, not a curated tourist experience.
The three main attractions are the Amber Museum, the 16th-century Fort San Felipe, and the Teleférico cable car up to the summit of Pico Isabel de Torres, where a Christ statue looks out over the coast and the green mountains behind the city. The views from the top on a clear day are excellent. The amber market near the museum is one of the better places in the country to buy genuine Dominican amber.
The local markets sell what many people consider the best pineapples in the world — the variety grown in this region is sweeter and more fragrant than anything you'll find exported. Pick one up and eat it on the spot. If you are staying at one of the beach resorts to the east, it is possible to walk along the beach to the city, passing Playa Bergantin along the way, which is mostly frequented by Dominicans and far less crowded than the resort beaches.
The surrounding region is worth exploring too: mountains covered in tropical vegetation rise just behind the city, and the coast has pockets of rainforest. Cabarete is 15 km east and worth an evening out.