During turtle hatching season you can visit Playa Grande at night in hopes of seeing a sea turtle come ashore and lay her eggs. We were told by the guide (you can't just go on your own - the turtles need to be protected from poachers) that the number of turtles on Playa Grande has steadily declined with the increase in tourism in Tamarindo. Normally we would have seen dozens of turtles, but we weren't lucky enough to see any on the night we went. YOu have the chance to go a second night for free if you didn't see turtles the first night, but it was our last night in Tamarindo. I'd definitely go back and try it again though!