When we visited Costa Rica, we enjoyed the Aerial Tram, which is a tram that slowly glides through the canopy and floor of the forest. The company that operates that tram ride also operates one in Dominica, so we decided to check it out. It was a very challenging drive to get there - probably one of the worst roads we drove in Dominica. To be honest, if we'd known how bad the drive was, we wouldn't have visited, or at least we wouldn't have tried to self-drive. Apparently the company that runs the tram will pick you up at your hotel, for a reasonable price, and we would highly recommend that option.
The tram itself is about $60 US per person, and the whole ride takes about an hour and a half. A naturalist/guide gets in the tram with you and your group (max 6 people), and if there isn't enough people to fill a tram, they will make you wait. The tram is only open on days when cruise ships are in town, so be sure to either look towards the port, or call ahead.
There is beautiful lush vegetation, amazing ferns and flowers, and a river hundreds of feet below that can be seen from the tram ride.
There aren't very many animals however (Dominica doesn't have any monkeys, and we didn't see any interesting birds either). At the top, there is an option to take a 20 minute walk down to the mid-point tram station. The hike is very easy, and takes you across a (fairly rigid) suspension bridge. The naturalist accompanying us was very well informed, and was able to answer all the questions we had about what we were seeing. In addition, she gave us a good introduction to Dominica.