The location you're looking for is the Citadel Stockade Point of Interest and it can be frustrating to find.
The following video shows the location:
You can take the Imperator's Waypoint and run down the ramps all the way down to the level where the Guild Registrar is.
Alternatively, you could run there from the Hero's Waypoint, which is already on the same level.
Look for the doorway with a symbol on it that looks like a locked jail door.
Run through that and down the ramp to the instance door for the Citadel Stockade.
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You see that little ^ next to the PoI?
That means that the PoI is above your current position.
Go up towards the top of the black citadel, keep going up, up, up.
You'll likely have to enter an instanced area, such as the points of interest in Divinity's Reach for Queen Jennah, and the spirit of the Pale Tree in The Grove.
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The one that appears to be just north of the Bane Waypoint is the Ash Tribune Quarters.
Take the Imperator's Waypoint, and head from there.
You'll find the instance entrance there.
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Here's an interactive guide to all the Points of Interest in the Black Citadel.
Just click the point you want to find on the map
and it will skip right to it :)
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The one you circled in your picture is called the "War Council".
It is up in the Imperator's Core.
When you go up the second ramp in the Black Citadel (the place where you talk to Rytlock), there is another instance in the stair way corridor.
It is right in front of you when you come up the ramp.
It will ask you to enter when you approach it.
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I've run around the "The Bane" area and inside the Core area, but I can't find the place to unlock this POI. How do I reach it?
How do I reach this point of interest in the Black Citadel?
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<guild-wars-2>
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Take the Imperator's Waypoint and run down the ramps. You can also go from the Hero's Waypoint which is on the same level. While hard to find, the location in question can be reached by teleporting to certain waypoints.
Instructions regarding the location.