Rita,

As mentioned before the Petroglyphs are located off the Reef Bay trail. The trail starts at Centerline Rd and winds down the mountain 3.6 miles until it hits the beach at Reef Bay. The Petroglyph trail is a spur located roughly 1/2 mile up from the beach. The National Park service offers a walking tour that comes down the entire length of the trail, visits the Petroglyphs and then visits the old sugar plantation ruins at the bottom (near the beach). They then provide transportation via boat back to Cruz Bay - which is worth every penny of the tour fee. Going back up the Reef Bay trail is one of the hardest hikes on STJ.

Reef Bay beach is steep and it does get a pretty good swell, I wouldn't recommend trying to beach a dingy there. Hope this helps.