An interesting further reading for Zion would be Isaiah 40:9 "O Zion, that bringest good tidings, get thee up into the high mountain; O Jerusalem, that bringest good tidings, lift up thy voice with strength; lift it up, be not afraid; say unto the cities of Judah, Behold your God!" To hear this sung, try "O thou that tellest good tidings to Zion" from Handel's "Messiah". Here is Marilyn Horne singing: https://www.youtube.com/watch?v=CSqNfnTAV3Q

In "The Pilgrim"s Progress", written by John Bunyan and published in 1678, The Celestial City is the "Desired Country" of pilgrims, heaven, the dwelling place of the "Lord of the Hill", God. It is situated on Mount Zion. So another way of saying it is "heaven" or "Heaven" or City of God. I do not know how widespread this awareness of the phrase now is in the English-speaking world, but all those who have been to a Church of England school or brought up in a Church of England family, would know of the book The Pilgrim's Progress and therefore The Celestial City. I would imagine that it is in the general studies or literature syllabus of most secular schools as well.

Other "place names" that have gone into the standard educated person's English vocabulary include such familiar phrases or names such as "Vanity Fair" and "The Valley of the Shadow of Death". There is also the Land of Beulah, which is a lush garden area just this side of the River of Death. Now the fashionable brand run by English aristocrat Lady Natasha Rufus Isaacs and fashion designer Lavinia Brennan is called Beulah. Many celebrities are customers, including the Duchess of Cambridge.

It depends on what you mean to suggest by the use of this term. "Celestial" can refer to the sky or planets in astronomy or to "heaven" in religion. A celestial city could be a metaphor for a real city seen at night from a plane or from space with its lights shining brightly like a galaxy. As you can see, the term has multiple meanings depending on the context in which it is used.