The Yokudan King NPC from the Secrets of the Lost City quest appears under the floor in the 2nd wisp hunting zone in the March of Sacrifices 4-man dungeon.
The quest marker appears for this NPC when the objective is to Retrieve the Cartulary, and it will only appear when getting close to this area.
I have only ever seen the Yokudan King appear improperly in March of Sacrifices and Hunter's Glade. Perhaps he has a niche for hanging around in Hircine's realm.
PC/NA — Lone Werewolf, the Templar Khajiit Werewolf
Werewolf Should be Allowed to Sneak