Officially better than you, according to PoN
I've been thinking about turning this into a proper mini-module.The Shade Pearl (The Lost Leagues)
Eyeball sized glass marble of unusual weight holding whirling white smoke. When uncovered and especially when held aloft it eats light cloaking the bearer in shadow (though not complete darkness). If already in darkness light from lanterns or infravision will not penetrate the darkness of the pearl. The peal is nearly indestructible and functions as a sling bullet+3, only if crushed against equipment of +3 enchantment (or similar) will it break.
If studied closely the smoke inside the pearl is revealed as clouds hanging over a miniature landscape of rolling forested mountains and a ruined castle. If you dress in bright colors and proclaim yourself light the pearl will absorb you into the pocket dimension called The Lost Leagues (roughly three 6-mile hexes in area), a barony removed from the world and put inside the pearl. It is now a monster haunted wood, dead if the pearl has been in the dark for too long or withered if thrown in a fire. The temperature will be warm whatever the state of the outside world. The state of their world is obvious to the inhabitants as the glassy ends of the world can be touched and peered through (dressing in black and proclaiming yourself shadow while touching the glass and you are thrown out). In the grand hall of the ruined castle rules the Howling Baron and his werewolf knights, if he is slain or if the pearl is destroyed The Lost Leagues regain the former size, inserting themselves back into the world with the ruined castle as the epicenter of where the pearl was.
Background: The Baron of Tarvale was a cruel and greedy man who eventuelly drove his subjects to rebellion. He and his men-at-arms put it down, still dripping with the blood of the rebels he adressed the assembled peasantry and cursed their thankless stingyness, swearing they and everything in his domain would remain with him forever. This turned him and his soldiers into werewolves and transformed the barony into the Pearl.
Situation: The people of Tarvale lived off of tar production. The baron has taxed every silver penny and ring and submerged them in a pool of tar, so that any would be slayer would be marked by it. In addition to his 30 werewolf knights a wolf pack also patrols the Leagues and they help the baron sadistically hunt down any real or imagined rebel, or invading adventurer. The baron still levies unfair taxes (nearly meaningless as there is no trade with the outside world) and those who can't pay have their relatives taken and devoured.
The dead in Tarvale do not find the afterlife. As the population and economy shrinks the woods reclaim the fields, the spirits of the dead reincarnate as anguished dryads in their image (perhaps inert trees wearing their faces?).
Necessary material to run:
Details on the weather, how the sky looks etc. in this bizarre dimension.
Details on The Howling Baron and his forces, The Curse, a map of the barony and the baron's stronhold.
Tactics of the Baron and his wolves, especially with regards to tracking and flushing out adventurers. Crossing streams to muddle tracks, fields of view in the valleys. Traitorous peasants?
How the peasants support the adventurers, a faction who likes the isolation the Pearl provides and wish to have the Baron imprisoned instead of slain.
Alternate solutions, what happens in the Barony is reintegrated into the world with the Baron alive? Would the Baron accept vassalage? Long term evolution of the Pearl if the situation isn't resolved. Timeline what happens if it is denied light to feed off. Can the peasants leave at all?
An abandoned hamlet (people seek to hide from the Baron), people who plan to slay the wolves (very illegal now, even self defense). The abandoned smithy where weapons could be silvered.
If you were to run this, what would you need or want?