Strolen's Citadel is an actual place of learning in the world- what is it like?

God has been slayed by a mortal man and his head is now worshipped and put on a pedestal. The PCs are hired to steal the head and bring it to a mystic that claims to have the power to revive God.

The PCs find a small green glass bottle, something can be seen writhing within the smoked glass. If the PCs open the bottle a repulsing form of life will pour forth and grow in size. A genderless beings of soft pliable purple flesh towers before the PCs, it has no detail, no distinguishing characteristics except for a narrow slit for a mouth that holds rows of inwardly curving teeth.

During a storm the PCs come upon a little boy that plays in the rain. Upon further inspection they discover that he has one eye and a long tongue lolling in its mouth. Spit dripping. It is a demon from beyond that can access our realm during storms, it eats all heads that are not its own, living and dead.

Moonlight shines down on the tranquil scene of a slumbering inn along one of the many roads that cross the land. Trees sway gently in the night air, and the stars twinkle brightly. All is quiet as the PCs snore away, a fine tendril of smoke curlsrnunder their door. The tavern is on fire! This is particularly bad news if the PCs own any horses - the screaming they hear is probably from their mounts! Panicky people are rushing about with buckets of water, trying to tame the flames. The fire fighting effort is not very coordinated as everybody is either hungover or still drunk, including the PCs. Hurry!

The PCs find a strange helmet, when donned it will take control of that PC and speak and act trough him/her. It explains that it is benevolent and needs their help in a quest and that it will stop possessing the PC when the task is done. Great if a player is gone for a number of sessions.

What if casting magic changed (for a few hours or days depending on the strength of the spell) the colour of the skin of the spellcaster? It could lead sadly to a very racist world to rp in.

As the PCs cross a brigde/tree over a deep river they see the glimmer of gold and jewels lying at the bottom. At further inspection they notice that it is the skeleton of a man still holding on to a sack of treasure. Will the PCs try to dive to get it? What killed the man? Did he simly not let go of the bag he could not swim to the surface with? What cleansed his bones so? Are there flesh-eating beings that dwell in the deep? Can the players resist the chanse of being wealthy for once?

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.

You find a patch of edible funghi. They taste well and all, no ill effects. UNLESS you consume some beverage, even 3 (three) days after eating it. Then you become really sick with pains, vomiting, all the fancy stuff. As a gift or good meal, it could be a cruel joke or to make sure the heroes spend their time focused on the mission. And the fine soup you had in the inn yesterday could have some in.
(Inspired through a real-world fungus. Was really used to cure alcoholism.)

Something lives in the fog in a certain region and travels with the fog. Kidnaps or kills, or is simply heard and "felt". ... fog is rising, heed the warnings the elders spoke!

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. Instead of city can be a traveller offering the food.

Mining in a certain area turns all exposed skin (maybe just parts that are actively disturbing the chemicals that cause the reaction) of the those doing the mining to a dark blue color. Will wear off taking as many years/days spent in the mine. ... meeting a party of blue-skinned humans armed with pick-axes etc. Strange disease? Demon offspring? Curse? If they meet only one ex-worker, they will very carefully listen to any stories he says, no matter if drunken or insane, or just makes up to get a beer.

Diseased people, (leprosy or any other such fear inducing disease) when traveling, will often times wear a cloak that entirely covers their body and ring a bell as they travel, used as a warning for any others to stay away. Could be used for a disguise or safe passage. ... you meet strangely cloaked people, sometimes ringing a bell. "Please give us something to eat, mighty heroes!" This is time to show how good they are.

Could come across a band of refugees. Could have been thrown out of their town by a tyrant taking of their land, bought out by somebody unexpectedly, fleeing a battle they know is coming their way. Could be proof of what they are searching for, hints and tips of what is to come, or just to broaden the reality of the world.

Young kid from last town has been following the PCs and doing a rather good job at it. PCs weren't expecting to be followed so weren't worried and the boy/girl was careful. Notice the follower a couple days out of town, kid ran out of food and started getting careless. Followed the 'mighty adventurers' to see if he could join them. Father is a wealthy merchant. Bring him home, bring him with, send him off? What do you do with an unwelcomed guest.

Rain slowly builds, thunder and lightning continue to roll in. Road muddies, horse/wagon getting stuck in the mud. Thunder strikes coinciding with a deep hole a horse just walked in, horse panics, breaks its leg (maybe just sprain?). Horse is decompacitated and the rain just went from pouring to an all out monsoon. Shelter needs to be found, horse needs to be taken care of, covered in mud, add the posibility of items being lost to the confusion with the wind and dealing with spooked animals.