Thousands of years of struggle and conquest have left the Warhammer world strewn with mystical relics, monuments and ruins. A battle will often be fought for the control or the defence of such a place, and for the awesome power it commands.
This is essentially a catch-all category for things that don't fit comfortably in other sections. Mystical Monuments are best treated as impassable terrain for the purposes of movement. Particularly large or complex Mystical Monuments might be made up of several terrain elements, such as hills or obstacles.