I'm 100% sure the eternal Christian heaven and hell are just fantasy, but I believe there are various heavens and hells, both physical and nonphysical places, in terms of great and prolonged joy or suffering. In the afterlife, you may end up in one or the other depending on what you think you deserve or what you expect. I believe Earth is a mild level of hell, at least for the human race (and an even worse hell for many animals under our subjugation).

Note that, since I believe everything imaginable exists somewhere, it would follow that heavens and hells as described by Christians must exist somewhere, they would just be a lot lot less common in the multiverse, they probably wouldn't be eternal (nothing lasts forever; the only constant is change), and they probably don't even exist on our timeline. Or, on second thought, some Christians probably create the Christian heaven or hell (more likely the heaven) in the afterlife based on their expectations, so it may be rather popular in our universe, though it still wouldn't actually be eternal, so technically it still wouldn't be the actual Christian heaven (or hell).