Café de Nuit

This is a question about Curse of Strahd and contains spoilers

In CoS, there are three missing magic gems that are used to produce three brands of wine by the Wizard of Wines winery. One is used by Baba Lysaga to power her hut, and one has been placed in that wooden Strahd effigy to animate the Tree Blight. Has anybody been able to locate where the third gem is?

It's up to the GM, they never state where it is. They do that quite a bit in that particular adventure. If it were me, I'd place it in the Abbey, you know the one, being used by the Abbot for his experiments.

It was left an unknown. All the Martikovs can tell the players is that it was stolen 10 years ago.

Here's an idea. In my game, I'm replacing the Order of the Silver Dragon with the Dawnslayers. The reason that vampires can walk in the daylight in my game is because the sky is always just hazy enough that the sun's rays are never direct. I wanted the players to get something for lighting the beacon in Argynostholt... but wanted it to be more than the paltry mechanical bonus the book gives them. I think I'll have the last gem in Castle Ravenloft and have it replace the dragon skull. If the party returns it to Argynvostholt and lights the beacon, I think that should clear the skies over Barovia and make sunlight dangerous to vampires again. The gems do seem to be tied to nature, so this feels particularly fitting.