Have a look at the Things To Do link at the top of this page for some ideas of whats available and see what takes your fancy. I would recommend doing a Round Island Tour.
We always use Tom Simo Ph (678) 7766572 Yellow Service Bus...very reliable guy for airport transfers too.....also available for private tours, day excursions, late night, early morning pick ups etc. He will meet you at the Port, take you where you would like to visit including, the Blue Lagoon, Eton Beach, a village or school, the Wahoo for lunch, Cascades and Tanna Coffee factory. You should be able to fit about 8 adults in the bus with your swimming gear etc. Pay for your own lunch (and his), entry fees to each place (its the only income a lot of these villages have) for about $130/day. Call to organise it before you depart. Bring some small toys, balls, old clothes etc for the ppl you will encounter on your way round :)
Edited: 4:52 am, February 02, 2014