I highly recommend going for a ride at Mozambique Horse Safari in Vilanculos. I went and had such a fun time. The people who run it were brilliant - it was very organised and well run. Worth every penny - I ended up riding nearly every day the views were awesome across the bay. The horses were really great.
Have loved Vilanculos - the best place i have been since i started backpacking through Mozambique
The only official taxi driver in Vilankulo is called Junior. Be careful with him, because he tries to get as much money as possible from you. Allways negotiate the price before getting in the car and make sure that the price is still same when you arrive!
Try to ask other transportation options from your accommodation or from staff and use those if possible.
take a boat trip from vilankulo, to one of the many beautiful islands then from there take a quick trip to the reef and snorkel on the inside of the reef, or do an amazing dive on the outer sides of the reef.