Termites, in certain places, make homes that can be eight meters high and only a half meter wide. They are built facing North to South to take advantages of the suns travel, maximum heat in the morning and evening and little in the afternoon. Imagine grassy plains with vertical structions facing a certain direction all over the place. Ambush? Maze? New creature? Larger structures?
Another real world thing. White tea. Can only be picked two days a year, the two days before the flowers blossom. Could be a similiar plant that...is the deadliest poison known, cure known diseases or psychosis, or a potent herb that just tastes awesome.
Small tavern in an out of the way town. Serve a wonderful delicacy that is simply outstanding. It is a creamy white consistancy, sweet, good to eat alone or a sweetener on any dessert.
If the explore or ask they are shown where they get it. They breed a group of large catipillars or some other type of insect that basically spit the product onto a setup that they created for that particular reason. Or maybe the delicacy is the byproduct of feeding them something.
Elves use nature as strength and borrow from the trees to keep them living. An elf out of the forest for more than a day begins to die and within 3 days is dead without borrowing the strength of nature.
A race that are always born as twins and only one recieves a soul. The other is soulless therefore without pity, shame, or guilt. The evil race. Can't tell them apart by looking at them.
A flower possibly in the plains or maybe all over that is always tilted towards a certain place. Sunflowers. Could possibly follow the sun or could be forever facing a certain position because of something that happened, either the air forcing it that way and it staying, the fire was so strong that the flowers faced away from it. It could be that in one spot a large fire was made or a fire war where many fire elementals were destroyed by the True Gods and radiating out from that point all of this flower is facing away from it so no matter where you are you always know where this place is by seeing which way the flower is facing away from.
Something lives in the fog in a certain region and travels with the fog. Kidnaps or kills, or is simply heard and "felt".
The local band of 'nasties' (goblins / orcs / whatever) lives in relative peace with the local population.
Along come the PCs and go through their usual heroic monster bashing routine, wiping out the nasties and pinching all their stuff, then continue on their way.
Problem is, they don't kill ALL he nasties. The survivors want revenge and, after spending a few months recovering, start to take it in their own inimitable style (which is not unlike that of the PCs come to think of it).
Next time the PCs are in the area they find themselves VERY unpopular with the townsfolk.