I am searching for Boris the Stout and several sources say he randomly appears in the cursed tombs. Where is this place? I am surprised that there is very little info on Google about this place.
I believe the "Cursed Tombs" are one of the maps you can buy from the map seller in the Mapworks (once you've beaten the game). Here's a screenshot:
That said, you can definitely find Borris the Stout randomly in other locations. Here's another screenshot showing him in one of the act 1 levels (the level in case you can't make it out is Watchweald Temple - Floor 2):