Rev 21:10

10 He carried me away in the Spirit to a great and high mountain, and shown me the holy city, Jerusalem, coming down out of heaven from God, 

carried me away in the Spirit – as in Rev 1:10, Rev 4:2; Rev 17:3, Ezek 11:1 etc.

a high mountain – the Sanctified Church as a mountain, see Isa 2:2, Mic 4:1-2, etc.

the holy City – described in Rev 11:2, Rev 12:1, and Rev 14:20.