From the pool área of the hotel you see Isla Garza on the left side.
Isla Garza is a 16 kilometer long undiscovered island with on one side the river Terraba (the longest river in Cost rica) and mangroves. On the ocean side is a beautiful long sandy beach.
You can walk for hours or just relax on this natural wonder.
Transport is by boat with a local resident. 
Just ask the reception to arrange this boat ride for you.