The state forest of Cambalache covers an area of just 1000 acres, making it smaller than a lot of Puerto Rican resort hotels. Almost halfway between Manatí and Arecibo, and west of Barceloneta, the forest is ecologically varied and characterized by distinctive karst formations; countless mogotes pop straight up from the landscape to heights of 160ft. Its many caves provide homes for fruit bats, which often swarm like bees into the evening sky.
The forest has a picnic area, 13km of hiking trails, two (poorly maintained) mountain bike trails and camping.
Note that a permit is required for cycling, but on our last visit there was no one checking for them and no way to obtain them in advance, except for calling the DRNA in San Juan. Basic on-the-ground information can be obtained at the often-closed ranger station to the right of the entrance gate.