When you visit the Cooks, plan to spend plenty of time on Aitutaki. It has one of the best lagoons in the pacific and the locals will treat you like family. The cache is located on "One Foot Island', which you will visit on any lagoon cruise that you take. Be sure to bring your passport to the motu (Small island) as they have a post office that will stamp it. Cache is an easy walk down the beach.
Small note on cache maintenance: I travel to Aitutaki from Rarotonga at least twice monthly for buisness and pleasure. I also have friends on the island that can help me to maintain it.