The Cecon-run Tortugario Monterrico is just a short walk east down the beach from the end of Calle Principal and then a block inland. Several endangered species of animals are raised here, including leatherback, olive ridley and green sea turtles, caimans and iguanas.
There's an interesting interpretative trail and a little museum with pickled displays in bottles. The staff offer lagoon trips, and night walks (Q50) from August to December to look for turtle eggs, and will accept volunteers. Around sunset nightly from September to January on the beach in front of the tortugario, workers release baby turtles. For a Q10 donation you can 'buy' a turtle and release it. Despite what everybody else is doing, please refrain from using flash cameras and flashlights.