Southeast of San Juan, the El Yunque National Forest (aka Caribbean National Forest or El Bosque Nacional del Caribe) is a lush paradise in the mountains. The best options for mountain biking are on abandoned roads, such as the following: 1) SR191 between kilometer marker 13.4 & 21; 2) SR930/FS27 (unsigned) one-way six miles; 3) SR915 and side excursion on TR#9.
To reach El Yunque National Forest from San Juan, head east on Highway 26 to Highway 66. Continue east on Highway 66 to Highway 3. Head east on Route 3 to Palmer. In Palmer, turn right heading south on Route 191 for 4.3km to the El Portal Tropical Forest Visitor Center. It is about 40km from San Juan.
Note: Mountain bikes and horses are not permitted on any trails within the El Yunque National Forest.
Overall, El Yunque National Forest is the 2nd most popular mountain bike trail of all 6 mountain biking rides in Puerto Rico.