A mystically roborant beverage brewed in some inconceivably arcane fashion by both the Ur-viles and the waynhim. Vitrim both looks, smells and tastes dusty - it probably sounds and feels dusty too, if truth be known, since no ur-vile or waynhim has ever been known to be any sort of expert cocktail mixologist. This is perhaps unsurprising, since the musty, fusty liquid seems to emerge directly (in bowls, of all things) from the bodies of the said Demondim-spawn. It's therefore almost certainly not a good idea to muse upon its exact nature, but instead to hold one's nose and quaff it down.
Like a surprising number of plot prop items in The Land - see particularly Aliantha and Amanibhavam - vitrim acts as a dramatic stimulant upon both humans and giants alike. It tends to make an appearance to save the day whenever the Good Guys™ are at the point of exhaustion in a particularly barren location, free of all vegetation. Given that it induces temporary energy and can provide at least an unawareness of and relief from all but the most grievous of wounds, some have opined that it must be a liquid form of crystal meth. Ur-viles in Breaking Bad, anyone?