“ The secret for immortality has been discovered by an eccentric wizard/mad scientist. Its found you need to reapply once a month. As people stop dying, and the birth rate increases exponentially, people are forced into homelessness, because of the need for food reamins the same, and food is not being produced fast enough to feed the undying population. The PCs have to find the creator and kill him, and destroy production, to save the world from undying, unending torture from hungryness.”
“ The extra-planar citadel of Ansern is named after its mage-founder. Ansern discovered the means to traverse the planar gulfs and created the citadel as a haven for his disciples in the art of planar-exploration. The disciples of Ansern continue his work and explore the countless worlds opened up to them by the work of the mage. They are cataloguing everything they discover in preparation for the greatest volume ever written: the Mondopedia, a book detailing many of the worlds. But the countlessness of the planes means that their book will never be finished.”
“ After the PCs defeat (or force the rapid retreat of) a villanous necromancer/demon summoner, they discover a book. This book outlines how to summon a demon whose power increases according to the size of the summoning circle used to summon it. And after the PCs examine a map of the country, they find that the layout of the cities and roads match up with the required summoning circle. In fact, the final road that would complete the circle is currently in construction.
With anyone who can find out about the circle and the ritual to summon the demon able to somehow make the final road/line, and destruction of the cities and roads currently in existence out of the question (unless this is an evil campaign- that removes the moral quandary), how are the PCs going to solve this problem?”