New Jerusalem · It is not on earth; it is the holy city John saw in Revelation coming down out of heaven from God, belonging to the new heaven and new earth.
The holy city coming down out of heaven at the climax of Revelation, also called “the Lamb's wife”; it bears God's glory, has 12 gates and 12 foundation stones, and has no temple because Jehovah and the Lamb are its temple.
Background
The New Jerusalem is the holy city seen by the apostle John in Revelation. He first saw a new heaven and a new earth with the sea no more, and the holy city, New Jerusalem, coming down out of heaven from God, “prepared as a bride adorned for her husband”; a voice from the throne declared that God's tent is with mankind and he will reside with them. An angel then carried John to a lofty mountain to view the city: a great high wall with 12 gates and 12 angels at them, the names of Israel's 12 tribes on the gates, and the wall's 12 foundation stones bearing the names of the Lamb's 12 apostles. John saw no temple in it, for Jehovah God the Almighty and the Lamb are its temple; nor does it need sun or moon, for God's glory illuminates it and the Lamb is its lamp. A river of water of life flows from the throne of God and of the Lamb, and on both sides stand trees of life yielding fruit each month, their leaves for healing the nations. Its gates never shut by day, and only those written in the Lamb's scroll of life may enter.
Related Scriptures (New World Translation)
And I saw a new heaven and a new earth; for the former heaven and the former earth had passed away, and the sea is no more. I also saw the holy city, New Jerusalem, coming down out of heaven from God and prepared as a bride adorned for her husband. With that I heard a loud voice from the throne say: “Look! The tent of God is with mankind, and he will reside with them, and they will be his people. And God himself will be with them.— Revelation 21:1-3
So he carried me away in the power of the spirit to a great and lofty mountain, and he showed me the holy city Jerusalem coming down out of heaven from God and having the glory of God. Its radiance was like a most precious stone, like a jasper stone shining crystal clear. It had a great and lofty wall and had 12 gates with 12 angels at the gates, and on the gates were inscribed the names of the 12 tribes of the sons of Israel. On the east were three gates, and on the north three gates, and on the south three gates, and on the west three gates. The wall of the city also had 12 foundation stones, and on them were the 12 names of the 12 apostles of the Lamb.— Revelation 21:10-14
And he showed me a river of water of life, clear as crystal, flowing out from the throne of God and of the Lamb down the middle of its main street. On both sides of the river were trees of life producing 12 crops of fruit, yielding their fruit each month. And the leaves of the trees were for the healing of the nations. And there will no longer be any curse. But the throne of God and of the Lamb will be in the city, and his slaves will offer him sacred service; and they will see his face, and his name will be on their foreheads. Also, night will be no more, and they have no need of lamplight or sunlight, for Jehovah God will shed light upon them, and they will rule as kings forever and ever.— Revelation 22:1-5