Location
The Cathedral is located at 1629W 1205S, fairly north of Roseborough between the west coast of the continent and the Stonewall Range. It is marked on your map when you explore the general area, and/or are walking between Roseborough and the Lethe Wyvern Sighting.
Area
The Broken Cathedral (Point 1) contains an Arcane chest (Point 2) guarded by some skeletons and Grim Shades.