"If the Eyes are the windows to the soul, then his soul was burning in Hell."
It was common belief in medieval times that goods and property could only be affected by the Fair Folk, the faeries, if it was acquired unlawfully or unfairly.
The gold hoops and rings that sailors wear are to throw into the sea if there is a storm. These are bribes to the sea gods to let them live through the storm.
Once a year, the king steps down from his throne, and lives as a peasant for one day, the next day is the anniversary of his coronation, and it is celebrated by a reenactment of the ceremony. This is doubly beneficial, firstly, because the people are able to have the grand parade that always precedes the ceremony. Secondly, because the heir to the throne is given a day on the job every year. Although, apparently, the thought has not yet come to one of the kingdoms enemies, the assassination of the king during the renewal coronation would be a moral, as well as a political blow to the kingdom.
A world where, instead of aging in years, the people age in knowledge. So, instead of dying once a general age was reached, they die once they achieve a certain amount of knowledge. A man could live forever if he never learned anything, or could die after reading a few choice books. Of course, the knowledge of the land would be regulated, like medical drugs.
What if a invisible person could see other invisible creatures? All you would need to do to check for nasties hiding around is turn invisible.
What if you send the players in a dungeon that was already raided? Maybe you could have traps that are already set off, or the corpses of monsters etc.
A place where an architect has built a temple/shrine to an evil god inside the walls of another building, a castle or another place of importance.
"Binding the Life Coil" is an ancient quasi-mystical technique rediscovered to prolong one's life at the expense of one reproductive ability. It is a simple magikal technique that anyone can learn (a skill or feat). The promise of near immortality or a lifespan of a thousand years or more makes everyone want to learn it.
This technique has a price though, the amount of immortality is in direct response to the strength of ones reproductive spirit. Those that have never breed will live longer than those that have. The use of the technique makes conception difficult, if not impossible. So you trade the future of your society for the chance for you to see much of that future.