The PC's stumble upon a village strangely devoid of life and activity, but they get the feeling they're being watched.
A noble claims that a stranger did not enter the town by any normal means, but trough his mirror. The man in question is ravening mad and mutters on about vast halls connecting all the mirrors in the world.
A certain type of toads, only found in the bleak swamps of Mournmist start falling on the city where the PC's are, like rain. Why?
The heroes are travelling the great seas by ship. One night when the seas are calm and everything seems fine their vessel is eaten by a great whale. The end? No. They wake in the belly of the animal, it is like a great cave. Full of wrecked ships and strange things to be discovered. Will they make it out alive?
The members of the party has unknowingly been infected by a mysterious plague and have been spreading the virus for quite some time now while adventuring. They start to hear rumors of all the cities in quarantine after they travelled trough. Will they discover the source of this? Will people start to avoid them, try to kill them?
A city the heroes visit is in a crisis, the king and queen are getting a divorce. Who shall rule? The inhabitants of the city take sides by tying a red or blue ribbon to their swords, sticks etc. Whose side will the Pcs take?
A plague is spreading trough the lands, the plague is actually an old woman carrying a stick. She walks from farm to farm spreading the plague. Can the PCs stop her without getting infected.
The party wakes up in an inn around a table with wine goblets near at hand. They have forgotten all that happened the last day. As they seek to find the truth they come in contact with a man that gives them a job which pays quite nicely.
When they have finished with this rather dubious assignment they are invited to dinner by the the man...
The PCs are sent with a diplomat to another country to protect him and do his bidding. There may be some espionage, rescuing, downright bullying, etc. Could make a nice medieval, special operations background.
One of the PC's falls in love with a woman who happens to be a necromancer...perhaps she/he is allied with a group working against the PCs?
A caravan is traveling through the desert. The party is hired to capture a man who is in the caravan, and it must be done quietly, so that nobody else knows. They are given the man's name, and the fact that he is a mage, but no other information about him. The catch is that the caravan consists of ten wagons, with at least thirty or forty guards.
A little way up the narrow valley, before they reach the woods, the PCs notice the squat, tumbledown buildings by the riverside. They are hardly big enough for a human to stand in, and the complex cogs and shafts that occupy the central cavity of one of the buildings are perplexing. What were these buildings? And how safe are they to explore?
Alternatively a desolate place is the perfect setting for a derelict chapel or croft. There needn't be any actual physical encounter involved, but it adds atmosphere to a place to see its dead history. For instance, in the Outer Hebrides there are whole deserted villages which were razed to the ground by the English during the Clearances. Such stories give a setting authenticity and character.