Well, it can't get much worse than the gulags that North Korea uses. From the Washington Post article linked above:
A distillation of testimony from survivors and former guards, newly published by the Korean Bar Association, details the daily lives of 200,000 political prisoners estimated to be in the camps: Eating a diet of mostly corn and salt, they lose their teeth, their gums turn black, their bones weaken and, as they age, they hunch over at the waist. Most work 12- to 15-hour days until they die of malnutrition-related illnesses, usually around the age of 50. Allowed just one set of clothes, they live and die in rags, without soap, socks, underclothes or sanitary napkins.
As the article points out, human rights in North Korea take a backseat, the efforts of Sam Brownback notwithstanding, to security issues in Northeast Asia. So if we're not going to intervene in North Korea, it's really hard to justify intervention pretty much anywhere else.