Grande Ile Mapou, British Indian Ocean Territory offers 1 beach perfect for sunbathing, surfing, swimming, and more. Grande Ile Mapou, British Overseas Territory, British Indian Ocean Territory, is known for its proximity to the Chagos Archipelago and the Diego Garcia military base. The best time to travel to Grande Ile Mapou, British Indian Ocean Territory, is from May to October, with average air temperatures around 27°C (81°F) and water temperatures around 26°C (79°F). Sandee provides detailed maps, photos, and reviews from fellow beachgoers to help you Choose Your Beach™ and plan your perfect beach vacation!