Where is heaven?
The Bible does not locate heaven anywhere in this created world. The heaven is where God resides in his absolute perfection. The Bible says “who alone has immortality, who dwells in unapproachable light, whom no one has ever seen or can see. To him be honor and eternal dominion. Amen." (1 Timothy 6:16, ESV)”.
We then will not reach God nor heaven through any space exploration programs nor through our minds.
He himself has stepped out from his hidden magnificence and revealed to us, what we need to know about heaven. The Bible—especially the Book of Revelation—has many depictions about heaven. These depictions cannot be fitted into one nice picture. How would a cube-like city full of golden streets look like? Or how would a never-ending, always renewing, hallowed worship look like? What about a garden, whose beauty is such that nothing compares to it? What does it mean that God himself dries tears from eyes? The old teachers of the Church have spoken of heaven as "the beatific vision" - when believers see God face to face in heaven. - At least for me this is already enough reasons to want to get to see it all!
And I heard a loud voice from the throne saying, “Behold, the dwelling place of God is with man. He will dwell with them, and they will be his people, and God himself will be with them as their God.
(Revelation 21:3, ESV)