The Brinktown jail is one of the most ingenious ever propounded by civic authorities. It must be remembered that Brinktown occupies the surface of a volcanic butte, overlooking a trackless jungle of quagmire, thorn, eel-vine skiver tussock. A single road leads from city down to jungle; the prisoner is merely locked out of the city. Escape is at his option; he may flee as far through the jungle as he sees fit: the entire continent is at his disposal. But no prisoner ever ventures far from the gate; and, when his presence is required, it is only necessary to unlock the gate and call his name.
Jack Vance, The Star King
innovation, jail, prison