A generation ago, King Æthelflyr ruled the city from a great castle that became occupied by monsters and haunted by demons during his reign. The King believed that if the castle was filled with confusing mazes and secret passages, the castle would not attract as many monsters and demons, so he hired several wizards to design and magically construct complex mazes throughout the castle.
When the wizards finished their job, they left town. Unfortunately, the wizards did their job a bit too well: it was now impossible to get to many of the places in the castle easily or safely, thanks to the presence of pits, intricate mazes, four-dimensional passages, and other diversions and dangers. The King and Queen both disappeared and were presumed to have gotten lost in the unfamiliar halls of the newly-convoluted castle. The disappearance of the King caused an uproar in the city.
Soon afterwards, the already-distressed city was attacked by heavily-armed warriors who were the best in the land. Even the city's well-trained knights were no match for them. The city's peasants and merchants attempted to flee; some were mercilessly slaughtered as they grabbed their belongings. After defeating the grossly outmatched castle guards in a matter of minutes, the warriors strolled casually into the castle and asked the castle workers where the treasury was stored. The workers did not know at all, since they were never told themselves, and so the warriors locked the workers in the castle cellar to starve to death.
Next, the warriors searched for the treasury. Because of the copious hazards present in the castle, all but one of the warriors died in the search. This remaining warrior was also a wizard and was known to have bouts of derangement.
After several years went by, a group of roaming merchants with modest magical skills found themselves drawn to the castle by curiosity, and began to explore the castle (perhaps against their better judgment). Upon returning from these expeditions, some merchants described visions of a wizard ensconced deep in the castle, clutching a very precious treasure. Others reported hearing the voice of someone challenging them to a fight, though it was not clear from what part of the castle this voice emerged. One merchant began to have recurring dreams of the castle suddenly springing back to its original state before it was altered by the hired wizards. Some attribute these accounts to mania induced by being bitten by too many flies (the castle is lousy with them), but your village has taken a less skeptical approach, and has appointed you to investigate whether there's anything behind these strange experiences.
Today you have the opportunity to get to the bottom of the castle's mysteries by venturing into its perplexing halls on your own. If this sounds too daunting, rest assured that you may have some help from the occasional roaming merchant (they trade in tools and services, and have a strange reputation for leaving food behind when they leave a place), and if all else fails you can re-start your journey at any time. Unfortunately, your village could not come up with enough funds to pay you a salary or purchase equipment for you; however, rumour has it that the castle is still loaded with treasures, so it could be a very lucrative expedition after all. Be sure to take it easy at first, seeing as you're a bit out of shape—your village couldn't afford physical training for you either—but with time you'll have the stamina to handle most of what the castle can throw at you. Above all, be creative, be persistent, and remember that things are not always what they seem to be.