Sterility Nadir
A Sterility Nadir is the metaphorically ‘lowest point’ of an extrasterile region that consists of a concentrated amalgamation of Sterility, usually spread out across a larger area and often, though not necessarily, situated at the physically lowest point of that same region.
Environment
Where masses of sterility converge, preternatural phenomena such as dark miasmas and vapours may manifest seemingly out of nowhere, accompanied by patches of black, brown, and grey lichen and moss, which, though not alive, yet grow. This is usually accompanied by a characteristic smell of tea.
Setting foot in such a place usually spells doom for whatever poor soul has had the misfortune of stumbling upon it. If that person happens to be extrafertile, their fertility may cancel with (some of) the surrounding sterility, often resulting in a violent explosion and, sometimes, the cleansing of the place.
In extreme cases, such places have been known to suck out fertility and sterility alike from those who enter them, paradoxically more rapidly the more extrafertile or extrasterile the person in question is; however, certain individuals seem to have devised a means of circumventing this effect, some with more success than others: Pliny the Elder is said to have survived by the skin of his teeth a venture into the catacombs below Mount Vesuvius, while Nuck Chorris braced the terrible depths of Grigory’s Abyme unscathed.