The Void Acropolis in WoW: Midnight appears to be reached by taking the portal found in the south of Val, then following the quest objective that sends you there. One guide specifically says to use the Void Portal toward the south of Val to enter the Void Acropolis.

What to do

  1. Progress far enough in the Midnight questline to unlock the related Void content.
  2. Go to the portal area in the south of Val.
  3. Use the Void Portal to enter the Void Acropolis.

Helpful note

If you are stuck on the quest step that says to go to the Void Acropolis, another player report says the objective may point you toward a building/portal interaction rather than a direct map marker, so checking the portal area carefully helps.

Related context

The same patch cycle also includes Void-related travel points for other activities, and guides mention that some Void content requires a short introductory questline before the portal becomes available.

If you want, I can also turn this into a quick step-by-step route from Silvermoon or Val.