If you want to travel around islands, or travel between islands you have several options: rental car, "Island" taxi (a modified pick-up truck with open bench seating in back), van-sized taxi, water-taxi, shuttle-sized bus, airplane, helicopter, seaplane, ferry, or on foot.
A rental car is probably your best bet for tooling around any of the islands. Rental cars are available at the airport and most of the major agencies are located there, as well as in the cruise-ship docking areas. If you are interested in off-road adventures you can rent a jeep or if you're staying local and want to have some fun you can rent a scooter to tool around town. Anyone not wishing to rent a car can take taxis to and from the airport or between destinations. If you plan on doing a lot of exploring however, you're probably better off with a car so you can come and go as you please. If you are planning to travel after dark to dinner at an unfamiliar location, it would be a good idea to scope it out during the day BEFORE trying to find it in the dark. Since parking is at a premium just about anywhere on the island it may be a good idea to inquire about its availability when making dinner reservations, or arranging for accommodations.
Things to seriously consider before deciding on rental cars or taxis might include: Driving on the left side of the roads can be overwhelming to first-timers, but after a few days it isn't too bad. Nearly ALL of the roads are very narrow, with no berms and few guardrails to keep one from going over the side. Steep inclines that make you feel like you will fall over backwards are commonplace, as are switchbacks or S-curves. Street signs are generally located on the left side of road, and many stop signs are barely visable due to vegetation overgrowth or lack of maintenance. Locals are prone to getting there in a hurry in spite of 'island time'. Night-time driving is specially hazardous because of lack of signage, lighting, roadway markings, and an abundance of first-timers who want to see the sights while trying to drive. Cell phone use is prohibited while driving, and seatbelts are mandatory for all. Some rental companies will not permit inter-island travel, so it is best to clarify that ahead of time. Make sure your own auto insurance will cover your driving rental cars in the Virgin Islands. Animals (cows, bulls, goats, chickens, iguanas, etc.) roaming freely also share the roadways and grazing areas alongside. Rush-hour traffic is just short of gridlock through the downtown areas. There are a few gridlock by-pass tricks that can be learned from islanders, but just remember you are on 'Island Time' so just slow down and enjoy it.
Walking is fine if you're planning to stay in one of the big cities but if you want to explore beyond the city limits, walking should not be an option. There just isn't room for pedestrians to safely walk on the 'country' roads. Many of the in-town routes are relatively flat but sidewalks can be quite rough or non-existent!
St. Thomas, St. Croix and St. John have public bus service. On St. Croix you can take a bus between the airport, Christiansted and Frederiksted. In St. Thomas there is bus service from the west end of the island, just past the airport, through Charlotte Amalie and to the East End of the island. The buses on St. John follow Centerline Rd. between Cruz Bay and Coral Bay.
To travel between islands you can fly or ferry. Be prepared to BACK ONTO the car ferry very slowly and carefully to avoid ripping out your exhaust system or worse. Some ferries are so tightly loaded that you may have to remain inside your car. If you are big on sea-worthiness, look for evidence of recent safety inspections while on your way across the sea. St. Thomas and St. Croix have airports and there are daily flights between the two islands. It's only about a 25-minute trip. There are seaplanes that make the voyage as well. Seaplane base is near Frenchtown area of Charlotte Amalie.
St. John doesn't have an airport but you can there by private boat or ferry. There are a couple of ferry services, some that take cars and others for pedestrians only. Check out Virgin Islands Fast Ferry or Love City Car Ferries for schedules and fares.
You can take the Water Island ferry between St. Thomas and Water Island as well.
