Hiking trails are maintained by the NPS. Trails range from short and relatively flat to down a tropical mountainside and back up if you desire or catch a boatride back to the NPS visitor center. You can literally hike the entire island. See my Off the Beaten Path tips for more on hiking trails.
National Park Service
Trailbandit hiking trail website
StJ offers an annual marathon. It is called 8 tuff miles
St. John Tradewinds article
There are many dive operators available on StJ Lowkey watersports is in Cruz Bay. They also offer equipment rentals.
You can also find snorkel, windsurfing, kayaking equipment rentals such as;
Cinnamon Bay watersports equipment rentals at the Cinnamon Bay campground
Cinnamon Bay Watersports
Crabby's watersport rentals in Coral Bay
As an excursion through our cruise ship, we went snorkeling on Trunk Bay beach. This was my first snorkeling experience and was very fun after figuring out how to breathe and do the fins. It seemed to be a great spot for a beginner to snorkel! And wow, what a beautiful beach!!
Equipment: We just brought our swimsuits and sunscreen and rented the snorkel equipment there at the beach.
Although my fiance had a little trouble with her snorkelling gear, once we were equipped properly, we really enjoyed our snorkel out in Trunk Bay cove. There is a very nice trail in the water for you to follow and see the flora and fauna.
Equipment: I would recommend renting the scuba gear from the National Park rental center there.
Everything you ever wanted in a resort! In my opinion, a hotel room is a hotel room and I didn't go...more
Our very exclusive package was ~$850 per night for seven nights. very secluded beaches, incredible...more
Maho Bay, off North Shore Rd, PO Box 310, , 00831, Caribbean