Dominica has many fun nature excursions and a lot less of your standard beach vacation as the rest of the Caribbean. Can’t speak on particular companies as I lived there and we went with locals however some top places to check out are Emerald pool (short east hike through jungle with huge natural pool and waterfall), Titou gorge, trafgar falls, and boiling lake (however this one is quite a steep hike).
Another idea that is much farther north from the port is explore Cabrits, an old fort (Fort Shirley) now national park.