Red Pit is a Vampire Counts resource building in Total War: Warhammer. Deep in the red pits can be found mercury in the raw form of cinnabar. A material often used in Dark Magic rituals.
Mercury is in demand throughout the Empire. In its raw form, it can be refined as pigment for clothing and inks. The Gold College will go to extensive lengths to obtain it - including striking secret deals with dark forces. Of course, Sylvanian residents have other uses for mercury, as it works well with Dark Magic - the two things bond extremely well.