Follow the posted roads from Liberia, CR, to the park. You will have to drive down an unpaved road at times (it can be accessed via a two-wheel drive rental car). You will probably encounter a manned “toll booth” (i.e., not offical at all) and have to pay the equivalent of $1 or $2 in local currency.
When you arrive at the National Park’s large visitor center, pay the entry fee and notify the attendant of your trail intentions. I was told at about 11am that I would only have time for one trail, not both trails, as I was “late” in the day and had to return by 3pm for the 4pm closing. I asked if I was at a bank! I am not used to closing hours at outdoor hiking paths. I took a number (so that they can verify that I returned) and proceeded to the Sandera las Pailas loop with geothermal features. Truly unique features and the jewel of the park. Against the advice of the visitor center, I proceeded to hike the Catarata de la Cangreja (waterfall trail). I ate lunch by a stream. We saw monkeys in the wild. Met Kristi and Anton from Canada, who swam near the waterfall. Total 12 miles of hiking. Trails are well marked, though the place is run poorly by Western standards. Weather: I visited in the dry season (February) and experienced warm, dry air. There was some very mild rain falling at parts of the trail, but it mostly evaporated before reaching my skin.