As reviewers have said before, Forestal Park is not well publicised in Tenerife, and not easily located on maps. There are no signposts until you actually arrive !! We drove from the south, cutting across from TF-1. Its far easier to take the slightly longer route and loop through La Esperanza and head straight into the Forest, where its located along the same road. Just in case, take their phone number and call if you get lost.
Also, this may have been mentioned before - Forestal Park is NOT OPEN to the public everyday. I think it was Wednesdays when they are just open for local school groups etc. Do phone first to check they are open to the public before you travel.
My thoughts of the experience echo other reviews on here, so no details needed from me, other than to say make sure you cover your legs, do not wear shorts as you may experience rope burn, not nice over sunburn!!!! Its a brilliant place to visit - 100% recommended.