1. Catamaran Cruise: There are plenty of boats around the port cities in the Dominican Republic, and almost all of them have small businesses that offer tours on sailboats and catamarans. Typically you can rent out the boat for a few hours and pay one lump sum. It's much cheaper if you can get a bunch of friends to join so you can all split the bill at a low rate for everyone.
2. Zipline: Getting off the coast, there are plenty of higher elevations that are perfect for those looking for a bit of adventure. At a fairly cheap price, you can zipline through the tree tops and don't worry it's perfectly safe.
3. Buggy Adventure: If you want to take a real look at the area, hop on a buggy adventure or a truck safari. These tours usually last an hour or so, and the tour guides can teach you a lot of interesting information.
4. Snorkel Trips: Snorkeling or scuba diving is a must while being in the Caribbean and the Dominican Republic is a great place to do it. Take a cruise along the Bavaro coastline, and the boat will drop you off at some of the most colorful reefs in the world.
Make sure you have a place to stay while you're in the area. Dominican Republic villa rentals are a great option for any size of accommodation. Just make sure you book your reservations well ahead of time!