Get here early as the sun can be punishing during the day. There were some interesting display boards and information in the visitors centre (if you look closely enough) and friendly staff to welcome you. They were happy to tell us about the park and explain where we should walk. (They even told us that there are plans to renovate the visitors centre and build an education centre, so 2013 should be an exciting time to go).
The longer walk is definitely worth taking extra time to do - the unstable dunes were stunning, providing a lunar landscape and a view over the interior on one side and out to sea the other.
The mahogany forest provided some welcome cool at the end of the walk and is filled with birds and butterflies for enthusiasts. There are also plenty of benches and bits of art, which add a nice touch.
These are the only sand dunes in Fiji (formed because there is no reef at the mouth of the Sigatoka river), so this is your only chance to see them.