The imposing steel and concrete building known here as Camp 6 once was the bane of Guantánamo detainees and human rights groups alike.

Built in 2005 for $38 million, it was a grim collection of darkened cellblocks where detainees were locked into their cells most days for 22 hours. Food was passed to the captives through a slot in the steel door, and guards peered inside every three minutes, to make sure none had hanged themselves. Lawyers said the rugged regime amounted to solitary confinement and drove the detainees mad.

Now, however, Camp 6 has become the lockup of choice for captives. Inmates can lounge in the cellblock, watching big screen televisions or chatting with each other. Meals, delivered in bulk, are parceled out by the detainees themselves and leftovers are stashed in a pantry in case a detainee feels the urge.