The coastal Guanica State Forest is known for its hiking trails and bird watching. There are miles of hiking trails, but you better expect it to be very hot and humid. There are over 100 species of birds and over 1,000 year old lignum vitae trees.
The main office for Guanica Forest Reserve is located at the end of Road #334 (not marked). A good place to start is the beach at the end of Road #333. The best time to hike is very early in the morning. Keep in mind that the reserve closes at 4pm.
Overall, Guanica Forest Reserve is the 10th most popular hiking trail of all 10 hikes in Puerto Rico.