Like I said, they vary. We don't normally get a heads up.
But um, since I've been here, there was a Clue-based scenario in WWII London (like, the board game), a Pokemon catching scenario for mostly younger specimens, a 19th century Romanian gothic novel type thing where they actually implanted false memories and motivations, a 1950s zombie scenario where it only infected men, and a dungeons and dragons-based scenario.
Between those, they generally change the compound for a while. We were in Central Park for a month, and Tampa for a few weeks, and a "Big Rock Candy Mountain" for a couple weeks, and a beach, and a sort of two week long rave.
They're I guess "rewards" but I kind of think they stretch the believability of the word there.