The Andamans have the clearest water in India and are the closest thing to a tropical island holiday without a passport. Radhanagar at sunset, scuba at Havelock, and slow cycle rides on Neil — the pace is unhurried and most of the trip is spent in the water.
Port Blair to Havelock (Swaraj Dweep) and Neil (Shaheed Dweep) runs on private catamaran ferries — Makruzz, Green Ocean and others. Book the whole group on the same sailing well in advance; seats sell out in season and the government ferry schedule is unreliable enough that it should not be a group plan.
Havelock has the best beginner dive sites in the country and no prior experience is needed for a supervised first dive. Groups get better rates when everyone books the same slot with one operator, and morning slots have calmer water. Elephant Beach is the standard snorkelling stop.
Flights to Port Blair are the biggest single cost, so booking early matters more here than anywhere else on this list. Mobile data is slow across the islands and often unusable on Neil — download maps, tickets and boarding passes before leaving Port Blair. Nothing on Havelock takes cards reliably, so carry cash.