The Realmgate is a part of Path of Exile 2‘s endgame, giving those who find it access to pinnacle bosses in the game. These foes are the strongest opponents you could possibly face, giving anyone with endgame builds the challenge of a lifetime. However, you can’t use the Realmgate until you understand where it shows up and how it functions.

https://screenrant.com/path-exile-2-find-use-realmgate/