I won't comment on the movie "Shawshank Redemption," but I will say this: The walls of older prisons could be quite thick. Take Alcatraz, for example. That prison became famous after a 1934 renovation that turned it into a state-of-the-art federal penitentiary. The renovation installed poured concrete walls a foot or less thick.

But before that renovation, Alcatraz was used as a military prison as well. This National Park Service cultural inventory has some details (PDF warning). Some sections of the military prison facilities incorporated fortifications built previously on the island, and the walls of those fortifications could be several feet thick, as they were designed to repel cannon fire.

Looking farther back in history, the walls of one of the world's most famous prisons, the Bastille, were five to 12 feet thick and built of stone.