From the farm drive back to the gas station (right turn from farm < right at first fork < through Villanueva and Naranjito). Go straight (be careful, you are supposed to stop here but the STOP sign tends to fall down.) As soon as you reach the town (Quepos) take a left turn – there will be a sign pointing towards Manuel Antonio. You will need to take one more left turn (follow the sign.) Drive 7 kms on this road until you reach the end of it. There are two parking lots (500-1000 colones depending on how much they tell you) and you can also park on the road by the beach. The National Park is just a few meters from the parking lots.