Where to find Valerian in Kingdom: Come Deliverance 2

The new Brushes with Death DLC for Kingdom Come: Deliverance 2 is pretty straightforward, but there's a point that might trip you up if you haven't been making potions or using herbs. Finding some Valerian for Kvyetoslava is a step in the Source of Inspiration quest, as you help the grandma recall the location of the shrine of Veles—a pagan monument that the painter is very interested in visiting.

Here I'll explain the quickest way to acquire some Valerian in this quest, but also more generally...