This is a scan of the printed map, which was distributed with the PC version of the game. It has more locations labeled than the map that was in the game, and shows more of the surrounding mountains.

This map created by Shrykull (Guilherme Coelho) compares actual in-game environments to the drawn map. It is rather large, both in pixel size and file size, so it may take a few moments to download.

Note from Shrykull: "The rules of architecture don’t even apply to BO1…As you can see, all the city of Avernus can’t possibly be placed at the given area.  I was lucky that at least most of the cathedral could be shown on the map! =P ...And the Plains of Blood I didn’t even remember.  But I can imagine they wouldn’t also fit there. Oh, and the Pillars are an “off-map” location, I placed them there because it was where they looked better."