Mariners Cave The waters between the islands of the Vava'u group are so blue, it's unbelievable. Some of the islands have sheer cliffs, others white sandy beaches. There are caves under water where you can dive or snorkel in. This cave is big enough to enter by boat.
Hiking the Cross-Island Track (Rarotonga). 'A Cook Islands sojourn usually involves lots of good eating and drinking, and lazy days on the beach. The perfect balance to this tropical relaxation is to challenge yourself on Rarotonga’s Cross-Island Track. The three- to four-hour hike via the 413m-high Te Rua Manga (The Needle) immerses walkers in some of the island’s most spectacular scenery.' http://www.lonelyplanet.com/rarotonga-and-the-cook-islands/rarotonga