Cinque Island is the gem of Andamans. If you find yourself stuck in Port Blair, I suggest take a trip to Cinque Island. It will take 2.5-3 hours to reach here from Port Blair, so one can easily plan a day trip to Cinque Island. But keep in mind that one needs a special permit from government to visit this island, and getting a permit can get somewhat tricky if you don't know anyone locally. Once at Cinque Island, you will have the whole island to indulge in some snorkeling and scuba. It is worth it, so do visit. you can get it through agency or if doing snoekling or scuba through some agency they may help you to get the permit.