Arrived on a Sunday to find that everywhere closed at mid day but we did not let this spoil our day.
We took a taxi from the port which cost us 15 euros each and did a tour of the tourist spots. This took about 4 hours in total and the driver was at our disposal the whole time. I would definitely recommend this over the on board excursions.
A visit to the gardens will cost you 5 euros to enter but the views are great and the plants and birds were lovely to see.
Although the tour is a set route if you wanted to add in other stops it would not have been a problem.