The players have a chance to cure the plague that has sprouted up upon their travels. Will they choose to do the right thing and help bring health back to the region?
Hidden above an alcove behind a forgotten waterfall could be one of the last intact temples of a long persecuted religious order dedicated to the worship of their water elemental patron.
To be used for the final encounter, find the final treasure, or anything that needs to be hidden away better then normal. Typical “who the heck would ever spend the time making it” but it is fun and a mental challenge for a change.
What about a 'criminal' society with distinct laws - for stealing, the larger the value of something stolen, the less punishment the courageous thief recieves (but must return it of course). For this pirates(?) caught petty thieves deserve to be punished harshly. If you take, you better take a lot.