Apart from the easy hiking in the shade of San Domino's pinewoods (the longest trails take only 30 min. end-to-end and never climb more than about 50m/164 ft.), the main activity for sporty types is diving. The best outfitter in the islands is Marlin Tremiti on San Domino at the Hotel Eden (tel. 0882/463765 or 0882/463211; www.marlintremiti.it).
The mostly shallow and remarkably transparent waters around the Tremiti present especially good opportunities for snorkelers and novice divers, though there are plenty of more challenging dives for experienced scuba enthusiasts. The entire area surrounding the Tremiti Islands has been protected since 1989, when the Riserva Marina Naturale Isole Tremiti was instituted here. The rich marine life includes octopus, lobster, congers and moray eels, grouper, dentex, bream, amberjack, even the occasional sea turtle, and the geologic formations below the water line are endlessly fascinating. Among the sunken relics off the Tremiti are remnants of a Roman ship (and its cargo) at Punta di Ponente, the southwestern tip of San Domino; the 19th-century steamer Lombardo; and at Cala Zio Cesare, a medieval ship that carried marble for the construction of the monastery on San Nicola. Deeper dives off San Domino take you to wreckage of planes and automobiles.
Off San Nicola, below the Torrione dei Cavalieri, is another Roman ship, at 50m (164 ft.) below the surface, with almost all of its cargo intact. Off Capraia, the Secca della Vedova and Secca di Punta Secca are medium-difficulty dives that show off the full range of typical Tremiti fauna and flora. Gli Archi is Capraia's most famous dive site, and its most difficult: At a depth of 60m (197 ft.), divers encounter a series of large natural rock arches opening onto diverse Mediterranean micro-habitats.
The religious-kitsch dive par excellence is found between Cretaccio and San Nicola, where a statue of Padre Pio, the immensely popular saint from the Pugliese town of Pietrelcina, is submerged at a depth of 15m (49 ft.). The 3-m tall (10-ft.) statue was sunk here in 1998, 4 years before Padre Pio was canonized.