On Tanna, there is the probably most accessible active volcano in the world. You may climb up to the crater rim and enjoy the spectacular fireworks.
Unfortunately, Port resolution, the best anchorage on Tanna, has been charted badly. So, approach carefully. Once there, you will soon meet the friendly people of Tanna. They are most helpful in providing you with fresh produce and clearing you in. Maybe you will have to go to Lenakel, which is a nasty ride on a 4-wheel drive truck, but a good way to see the Island.
When you are lucky, you may be able to attend the Nekowiar ceremony, which is three days of gift giving, singing and dancing.