Puerto Plata is old, a little dirty, and there are motor scooters EVERYWHERE, including possibly the sidewalk. Traffic signals, when they were introduced, were treated as an indication that the power was on that day. The locals are a little better obeying them now, but it’s best to look in all directions before moving anywhere. The tonnage rule is in full effect and pedestrians are at the bottom of the pecking order. Just be fully aware of what’s around you and you’ll be fine.
The Marien is just outside the Playa Dorada complex, but it’s an easy walk. Playa Dorada is a gated area and as such is pretty safe and nice to walk around. Overall the beach is nice, but not spectacular. There is a bit of wave action so there won’t be snorkeling off the beach. The water isn’t all that clear so there’s not much to see anyway. Snorkeling is a lot better up towards the Grand Paradise (about a 15 minute walk) since it’s calmer and the sand is coarser and doesn’t stay in suspension for long. Sosua and Cabarete are definitely worth the visit. Snorkeling in Sosua is usually excellent.
There are plenty of varied excursions to take. Towns and villages in the area are interesting to visit. Don’t miss the cable car up Mt. Isabelle de Torres (793 metres high). There’s a nice botanical garden at the summit. The view is spectacular. Just go there early in the morning as the mountain is generally clouded over in the afternoons. Ocean World is another not to be missed place. I have done business with a local tour operator (Martin Espinal). His English is perfect and he had good equipment. If he’s still in business, I highly recommend him. You won’t find him listed under that name. If you want to go touring with him, drop me a line and I can give you contact information.