There is a lot to visit on the island. I've been there five times now and still haven't seen everything. I advise you to get a good travel book. Read a bit and then narrow down depending on how much time you have and according to your personal interests.
Since you're in Trou d'Eau Douce, you're close to the Deer Island (Ile aux Cerfs). Go there early, because it gets crowded towards midday.
You can also find lots of info online. Here's just one URL:
http://www.gov.mu/portal/site/Noncitize ... 800b521ca/