What happens after we die has been seen metaphorically by a few astral travelers. What I think is key to understanding the entire cycle of birth/life/death is to understand why it is souls incarnate.
Incarnation is a phase of existence we go through when we're self-aware enough to have a sense of free will, but not self-aware enough to be able to sustain ourselves indefinitely in an eternal context. Before we lead programmed existences as animals/plants. We have enough consciousness to have 'personalities' in the same way a dog has personality. To affect certain aspects of your life.
This self-awareness blossoms into what we call intelligence. The intelligence we possess isn't yet mature, mature intelligence is called spirituality. The intelligence we possess is flawed, prone to going every which way and that. Intelligence is dangerous to itself.
So this process of incarnation happens where we can learn lessons from our self-defeating mistakes within relative safety. We die and are reborn constantly. The lessons get progressively more and more subtler and refined, until we finally have shed the need for the birth/death cycle.
The souls themselves are eternal and unchanging. It's the incarnations that form beliefs in God or beliefs in the lack of deity. These beliefs are localized to that incarnation, they don't affect the soul's journey at all.
Now, the body is composed of physical as well as etheric matter. When the body dies, the incarnation gets shunted off into the ether. In the ether the incarnation can continue, for a brief time, while it can still maintain itself.
This is difficult for most incarnations because timelessness can't yet be understood or held on to. So eventually the etheric matter fades away into a pure observation mode where it observes the effects it had on the world, it's descendants, until it gets tired of existing and fades back into its true soul.
Now, some incarnations develop this intense belief in a Heaven or a Hell. The intensity of these beliefs orders that soul's afterlife. If the incarnations believe they truly deserve to go to Hell, well, Hell is a certain place in the ether they can visit, for as long as they want to be there. Heaven exists too.
In either case, the incarnation eventually tires of eternality and fades back into its soul.
Atheists, having no particular beliefs about the afterlife, will be surprised to find themselves in an afterlife. They can explore the ether for as long as they wish, just like everyone else, before fading back into their soul.