This community-run project just north of Punta Pérula lets you camp and watch (with local guides) the turtles nest. It's become a destination for international students interested in turtles and their habitat, and offers volunteering programs. You'll need a vehicle to get here, or you can visit the camp on an overnight trip offered by Mex-Eco Tours.
You can camp here year-round, but July through November is the best time for turtle sightings.