There are two main operators, that offer cruises to the beautiful Muri Lagoon: Captain Tama´s and Koka´s. Both seem ok, so no worries. The Lagoon itself is located to the South East of Rarotonga. The tours offer an entertaining and educational mix about the local culture, coconuts, sarongs (there are 374 ways to wear them) – and of course you can snorkel to your hearts content. Food is superb (fresh tuna steaks) and there is always the happy tune of Cook Island music. Just don´t be bothered to be sharing a glass bottom boat with 20+ people.
“Aitutaki´s stunning lagoon, brimming with marine life and ringed by 15 palm-covered islands, is one of the treasures of the South Pacific” (Excerpt from the Lonely Planet Travel Guide). We agree. My wife and I rated it as one of the most beautiful places we have experienced.