“ 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.”
“ The PCs are accosted in a major city containing at least one famous fortuneteller / prophet of the future. They are informed that their as-yet-unborn child will (insert terrible evil), and that, although they are very sorry, the PC must be executed to keep this from happening.”
“ A huge moon, with a three-coned volcano which can be seen from the planet when it erupts and is taken for an omen. The planet, smaller than the moon, orbits it, and the planet in turn is orbited by a very small but very hot and bright ball of flame.”