The Undercity is tied to a side quest, that you’ll get from Ormus in the Council Chamber when you finally get there as you progress through the campaign. Also read: Diablo 4 Vessel of Hatred ...

With the new Undercity feature in Diablo 4 Vessel of Hatred ... It’s a Priority mission and you will need to speak to Ormus in the Council Chambers. Burn through his dialogs and then make ...