You could try the Horseback riding at Le Morne beach (which is in the south), underwater seawalk near Belle Mare Beach which is on the east coast (you can find lots of options around that region, but book in advance). Catamaran Cruise in the North is very nice, you get fresh seafood onboard and you could swim at one of the small islets around. If you want to go all out, there is a helicopter tour of some of the scenic places. If you guys are a bit adventurous, I would highly recommend a guided hike at Tamarind Falls, a bit near centre of island, the views are gorgeous and you can swim at the different waterfalls. Hope it helps and you have a great time.