Turtle dragons are inhabitants of an ocean in Dragon Land. They are like turtles, only with the tail and head of a dragon.
They only lay eggs inside sandcastles, so they'll only arrive where there are any. If, for any reason, the sandcastles are destroyed (either by waves or the footsteps of Mr. Giant arriving to see them), they leave to lay them somewhere else.
A drawback is they can't see well in the dark, so it is better done before the sun sets. On the other hand, to get them anyway, fire breath helps.