“ The PCs come across a wild thicket of luscious looking blackberries. They eat the berries and become drunken fools. Later they find out that the berries were part of a fae garden and were intended for fae wine. In payment for stealing the berries, the mischievious fae make life inconvenient for the PCs. Horses are untied, water skins are drained, spare clothing is drug into the water, etc.”
“ The city was cursed many years ago. Since then it has not stopped raining. The gutters are inhabited by eels and the doors are on the first floor, coated with pitch. On a bad day, you can see the water level rise above the ground floor windows. Carts have both wheels and bladders filled with air to keep them afloat. And yet everyone is surprisingly dry.”
“ While it is within your purview to write long-spanning histories of your world, it is largely unnecessary. If you are running an RPG, do this instead: make a bullet point list of important events that affect the world today, and mysteries that people still don't know. Let these fuel your adventures.”