It may be tiny, but Giannutri has some of the best diving in the Med. Rich marine flora and fauna include vast "prairies" of posidonia (Mediterranean sea grass), coral, sponges, sea urchins, seahorses, starfish, amberjack, grouper, lobster, and, on rare occasions, turtles and dolphins. The island's 11km (7-mile) coastline is riddled with crevices and grottoes that make for spectacular underwater viewing. At Punta Secca, two cannons from an 18th-century galleon rest 50m (164 ft.) below on the seafloor. Near Cala Maestra, you can dive among the wreck of the Nasim II, a 69m (228-ft.) freighter that hit the rocks and sank here in 1976. It was carrying 49 cars and 16 tow trucks, and much of the cargo -- that which wasn't looted in the immediate aftermath of the accident -- remains strewn on the seafloor between 33m and 60m (108 ft.-197 ft.). At Cala Ischaiola, you can dive down to the shipwreck of the Anna Bianca, a cargo vessel that went down in a matter of minutes in 1971. The Archetti (natural rock arches, 10m/33 ft. below the surface) are another popular spot with wonderful light effects, and eels and scorpionfish among the cracks.
A number of Argentario-based diving operators organize excursions to Giannutri. Try Argentario Divers, Piazza San Sebastiano 60, Porto Ercole (tel. 0564/832024; www.argentariodivers.it), or Abisso Blu, Via Marconi 66, Porto Santo Stefano (tel. 333/3826314; www.abissoblu.it).
Giannutri's small size and relative flatness (the highest point is 88m/289 ft. above sea level) make it attractive for even reluctant walkers. Much of Giannutri, even the wildest terrain overgrown with macchia, is privately owned, but there are two perpendicular paths open to the public.