We live in a three-dimensional reality, and if our three-dimensional reality is embedded in a 500-dimensional space, then our three-dimensional reality and some other three-dimensional reality will coexist in that 500-dimensional space, but we would never know about the other one.
And to use that idea for your fictional superhero narrative is just totally awesome.
But what Marvel did that was great was, they just brought up that idea — that you may have a universe of infinite spatial dimensions, and each of the different subsets of those spatial dimensions could be a separate universe.