There are no roads to Tortuguero and no cars in it: you arrive by boat from La Pavona or Moín, or by small plane, and once there everything happens on the water or on foot.
The canal tour at dawn is the thing to do, ideally in a paddled or electric boat rather than an outboard. Green turtles nest between July and October and the nesting tour is tightly regulated — licensed guide, permit, no torches, no cameras — which is exactly why it still works.