Landlubbers looking to explore inland Vieques [1] can get a guided, off-the-beaten-path mountain-bike tour with Vieques Adventure Company (69 Calle Orquideas, Esperanza, 787/692-9162, garry [at] ciequesadventures [dot] com, www.bikevieques.com [2]). Bikes rent for $35 a day ($25 a day for multiple days) and include a helmet, a lock, and a trail repair kit. Half-day tours are $75. Combination bike-kayak-snorkel tours are also available.
Links:
[1] http://www.moon.com/destinations/puerto-rico/vieques-and-culebra/vieques
[2] http://www.bikevieques.com