To get to Vieques [1] and Culebra [2], you can fly from Ceiba or San Juan [3] or take a ferry from Fajardo [4]. If you’re visiting for only a day or two, spring for the airfare to save time.
Although it’s possible to get to your hotel and some of the islands’ beaches using publicos (shared vans that carry multiple fares at a time), to fully explore the islands’ remote beaches a rental car is recommended. Book early though, because they go fast.
Vieques [1] and Culebra [2] are such small islands that it’s possible to spend a day and a night on each one to get a cursory feel for them both. But the reason most people go is to experience the islands’ unparalleled natural beauty and soak up plenty of R&R. To do those things properly, it takes a few days to reset your internal clock to “island time” and achieve a blissful state of total relaxation.
Links:
[1] http://www.moon.com/destinations/puerto-rico/vieques-and-culebra/vieques
[2] http://www.moon.com/destinations/puerto-rico/vieques-and-culebra/culebra
[3] http://www.moon.com/destinations/puerto-rico/san-juan
[4] http://www.moon.com/destinations/puerto-rico/east-coast/fajardo