The EN World kitten
Citadel Cavitius, on the Quasielemental Plane of Ash, which was originally detailed in WGA4 Vecna Lives!. After he was pulled into Ravenloft (as recounted in Domains of Dread), the citadel was said in The Inner Planes to have been left behind (and revealed that before Vecna took it over, it belonged to Sigil's Doomguard faction as one of their fortresses on the negative quasielemental planes).Doesn’t Vecna have a prison on one of the planes detailed in the original Planescape box? Memory failing here
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