Originally posted by Ryzilynt:

I usually find the vesigvir near a "stonehenge" looking structure in the plains.

That said , i usually find the alter first.

Heh... pretty much this. On my current world I've found two Yagluth altars thru pure exploration. I guess it's kind of a vegvisir that's on the (any) altar itself. It will place the boss marker on your map if it isn't already there. Fortunately Yagluth's altar is hard to miss.