One of the Doomguard's four negative quasielemental headquarters, Citadel Exhalus (also known as the Portal of Last Breath) is found in the plane of Vacuum. Unlike the other citadels, Citadel Exhalus floats free unanchored to any solid ground; without any true borders in Vacuum, nor with any significant islands of solid matter, the fortress is instead constructed around a portal to the Negative Energy Plane, an ethereal conduit running between the two planes and tethering the citadel in place. Here, many Doomguard come to look upon what many see as the ultimate result of the entropy they respect so highly, as well as a number of Dustmen guests coming perhaps as close to existence in the Negative Plane without protection as they can. Citadel Exhalus is led by the terse Doomlord Nagaul, and following her lead, the citadel is dominated by that branch of the Doomguard seeking the acceleration of entropy so as to sooner reach that eventual end.
- Factol's Manifesto, pg.43
- The Inner Planes, pp.124-125
- Planescape Campaign Setting: A DM's Guide to the Planes, pg.37
- Planewalker's Handbook, pg.29