The easiest way to access the caches is by kayak. You can book a kayak tour from one of the tour operators in the area (Bahia Rica Fishing & Kayak Lodge). Or you can hire one of the local fishermen to take you around by boat. The route is approximately 10 km, so if you opt for kayaking you should schedule at least 4 – 5 hours.
All the caches are close to the water in the public zone. In Costa Rica the first 50 meters from the water is all public.
Make sure to bring water, sunscreen and a hat!
There is a campsite on this beach at Isla Jesusita. if you want a full adventure you can even stay overnight here. Just talk to Alex the manager on beforehand to book (Note! he only speaks Spanish ;o): +(506)8605-0657 There are also dogs here, and they might come barking at you, but just call them with a friendly voice and the barking soon turns into tail vagging and begging for a snack.
Enjoy!