Sam isn't sure what he's expecting to find after he lands in hell. He knew it wouldn't be pleasant; it is hell after all. Perhaps, subconsciously, he'd been expecting the usual fire and brimstone backed by screams of the damned.
But there's just nothing.
There is no sound, no light, no heat, no cold. The nothingness is so oppressing Sam can't even hear the sound of his own breathing. If he even is breathing. He supposes that technically he's dead now, and usually the dead don't breathe.
Sam can't tell if he's standing or sitting, if there's any ground around him anywhere. He brings his hand up and waves it in front of his face, but he can't make out anything. There's no light to see his hand and he can't even feel the breeze the small movement should have created.
Something starts niggling at the back of Sam's neck, as if someone is watching him. He turns his head, trying to see if there's anything behind him, but only the blackness is there.
Sam doesn't even know how far the void extends. He could be in a room that's barely big enough to fit him or it could stretch on for miles. Sam isn't sure he wants to find out either way.
He tries to calm himself, tell himself that what he did was good and right; it was the only option they had. When Sam thinks about it, he would do it again. He saved the world and stopped the apocalypse. If he has to spend an eternity in hell for his actions, it's a small price to pay.
That tingling sensation is back and Sam whips his head around, trying to catch whatever it is. But once more, he sees nothing.
He will always see nothing, hear nothing, feel nothing.
This is his punishment: an eternity of nothing.