here is some useful information on how to reach Drake Bay and the North of the Peninsula
There are several ways of traveling to Corcovado National Park. It depends on how much time a traveler wants to spend traveling there, or from where the traveler is coming from. The fastest way is definitely flying from San Jose to Drake Bay or Palmar Sur, a flight that lasts for around 45 minutes. If you fly and land in Palmar Sur, there is only a 15 minute boat transfer from the airstrip to the lodge. If you land in Palmar Sur, you must catch a taxi to Sierpe ( 15 minutes ) and take the boat ( private or public ), and travel/explore the majestic river until reaching the ocean, and 15 minutes after, Drake Bay. This track between Sierpe and Drake is very nice and interesting, almost a tour by itself, since you will cross the entire Mangrove Forests.
Another option is traveling by land, in which case you should drive to Sierpe. There, you can leave the rental car at the local parking lot ( Cost of 7 U$ per day ) and catch the 11 AM or 3 PM public boat, or in case of a package, you will be indicated the departure time in advance. During the dry season, you can also drive to Drake Bay, but since you need to cross several rivers, it is a bit more adventurous.