There is a city that was built over another city, the superior counsel insisted on building it because of a 'illness' that was spreading. They left people who were still 'infected' down below. It is forbidden to go there because of the "monstrous mutants" that have developed throughout two millennium. The superior counsel refers to it as the underworld. Those who get the chance to go actually named it the down below. If you do go to the down below, be ready for the buried secrets of the town.