A long day-trip from Nosy Be — about two hours each way by speedboat — Nosy Iranja is two small islands joined at low tide by a wide white sandbar you can walk between. Green turtles lay their eggs on the beaches, and the snorkelling on the surrounding reef is excellent.
The catch is the crowd: most operators run Iranja as a packaged outing and you may share the sandbar with a dozen other boats. The lighthouse on the larger island, with its Eiffel pedigree, is a short walk inland. Go on a weekday and bring sun cover — there is little natural shade.