Kalkstein's laboratory is where we find our favourite alchemist in Old Vizima in Act V of The Witcher. The neighbourhood has definitely gone downhill. Here, cemetaurs and graveirs regularly congregate in the alley just outside Kalkstein's door.
His accommodations there are much more modest than even his Temple Quarter domicile. As with his other home, Kalkstein is generous with his space here too and allows the witcher to stay here anytime in Act V.