An adult loggerhead can be over a metre long and weigh around 130 kilograms. They spend most of their lives swimming far out in the open sea. But every two or three years, the female turtles come back to the same beach where they themselves were born - and they crawl up the sand in the dark to dig a nest.
She uses her back flippers to dig a hole about half a metre deep, lays around 100 round eggs the size of ping-pong balls, then covers them with sand and goes back to the sea. The nest is left to itself. The sand keeps the eggs warm for about two months. Then, one night, the babies hatch.
A tiny baby turtle is barely the size of your palm. It pushes up through the sand with the others - sometimes 80 or 90 from one nest - and they all rush to the sea together, following the brightest light, which should be the moon shining on the water. Once they reach the sea, they swim out and won't come back to land for years.
Greek schools and volunteers help keep the beaches safe at hatching time. They mark off the nest areas, ask people not to use bright torches at night (which can confuse the babies into walking the wrong way), and clear the sand of anything that might block their tiny journey.