The next day we checked out of Roseau and went on a driving tour of the island. Our first stop was Emerald Pool, a UNESCO World Heritage Site in Morne Trois Pitons. These are the most accesible falls in Dominica. On cruise ship days, I'm sure it's very busy, but we were lucky enough to visit on a non-cruise-ship day and so there was only a couple of other people. There is about a 15 minute easy walk from the parking lot (with a restaurant, souvenir stands, and toilets) to the falls themselvs. The falls empty into a pool of water, which begs to be jumped into.
We avoided the temptation to take a dip as we were worried about bilharzaia / schistosomiasis, but a Canadian doctor we met later who teaches at the medical school in Portsmouth assured us it wouldn't have been an issue.