The new Heaven and new Earth are just as real as anything in the Bible. John the revelator son of zebedee gave a very detailed account of the new heaven
Apoc 21 - the introduction of the New Jerusalem parallels the vision of the harlot city, the Old Jerusalem. This also closely follows what we read in Ezekiel of his vision of the temple in the latter days (Ezek 40)
The New Temple has the “glory of God” - the cloud of the Spirit’s presence.
The city 21:12-14 is perfectly symmetrial with three gates on each of the 4 sides, like Ezekiel’s vision. The total number of gates, 12 is symbolically significant — as, just as in Ezekiel’s vision, each of the gates has the name of one of hte 12 tribes (Ezek 48:31-34; Apoc. 21:12).
This signifies that Israel was the gate through which God’s promises to entire humanity comes.
Note; a perfect cube is the city - the same length and breadth and height - refer 1 Kins 6:20 — the New Jerusalem is one giant temple where all who dwell within it live in the most sacred presence of God
Then in Apoc 21:22 we see AND I SAW NO TEMPLE IN THE CITY, FOR ITS TEMPLE IS THE LORD GOD THE ALMIGHTY AND THE LAMB — the Lord IS the Temple.
All of this is symbolic - talking of the church as the new Jerusalem - the book of the Apocalypse is the grand culmination of the story starting from teh book of Genesis