A fine outing on St. John is a boat trip to one or more choice snorkeling spots.
Climb aboard the Sadie Sea for a tour with multiple snorkel stops. As a bonus, guide/owner Sandy West tells great island tales.
Though the snorkeling doesn't match Buck Island (above), you'll see lovely coral and fish and the variety of visiting three different spots is fun, as is the boat trip itself: a lovely way to enjoy the sun, sea, and seabirds.
