The Bible doesn't always give us the full details that we want; one question it leaves us with is where Jesus went when he ascended, body and soul.
The Gospel of Luke simply states that he was taken up into "heaven."
Then he led them out as far as Bethany, and lifting up his hands he blessed them. While he blessed them, he parted from them and was carried up into heaven.
The same question applies to Mary's body, as the dogma of the Assumption states that she was also taken to heaven, body and soul.
The Catechism of the Catholic Church asserts that "heaven" is not a physical place that we can travel to or locate on a map.
This biblical expression [Who art in heaven] does not mean a place (“space”), but a way of being; it does not mean that God is distant, but majestic. Our Father is not “elsewhere”: he transcends everything we can conceive of his holiness. It is precisely because he is thrice holy that he is so close to the humble and contrite heart.
St. Thomas Aquinas' solution
St. Thomas Aquinas reflected on this topic in his Summa Theologiae and gave the following argument as to "where" Jesus' body is, since it is a physical body, but is not currently in the created world.
A place implies the notion of containing; hence the first container has the formality of first place, and such is the first heaven. Therefore bodies need in themselves to be in a place, in so far as they are contained by a heavenly body.
But glorified bodies, Christ's especially, do not stand in need of being so contained, because they draw nothing from the heavenly bodies, but from God through the soul. So there is nothing to prevent Christ's body from being beyond the containing radius of the heavenly bodies, and not in a containing place.
Nor is there need for a vacuum to exist outside heaven, since there is no place there, nor is there any potentiality susceptive of a body, but the potentiality of reaching thither lies in Christ. So when Aristotle proves (De Coelo ii) that there is no body beyond heaven, this must be understood of bodies which are in a state of pure nature, as is seen from the proofs.
Basically, Aquinas argues that there exists something "beyond" the universe. This doesn't mean you can fly to it in a spaceship, but that it is outside of time and space.
This "place" (for lack of a better word) is where glorified bodies dwell until the end of the world.
Another dimension?
As humans, we don't have accurate words to describe what this would be like. Some medieval Christians thought there were various "spheres" that surrounded the earth.
Other theologians have described this "uncontained place" as a different "dimension."
While this isn't a good analogy, our modern imaginations might think of this in a similar way as Marvel's "muti-verse," which is essentially another plane of existence that is "outside" our universe. The only way we can "travel" to it is by the route of death.
J.R.R. Tolkien wrote a medieval view of death in a similar poetic way in his Lord of the Rings epic. In his mythology there was a place called Valinor, which was originally connected to the world "in the beginning," but was then disconnected and existed outside of it. Special ships could take a person there via a "Straight Road," but these ships essentially represented a person's death, as they could never return to Middle Earth.
Both of the above images are inaccurate, but they can help us in some way try to understand something being outside of the known universe.
A mystery
God never gave us a map or coordinates on how to reach "heaven," but he did give us a compass.
That compass is the Bible and the good news is that through Jesus, we can reach heaven when our lives on earth are ended.
It is a great mystery as to the location of Jesus' and Mary's body, but a mystery we will encounter when we die.
