From Rule book 2.0 page 17
Line of Sight
In order to cast a spell or make a ranged attack against a target, you must have a clear “line of sight”
(called “LoS” for short). Normally, a creature has LoS to the entire game board, even into zones that
are out of range. But, some walls block LoS. You cannot cast a spell or make a ranged attack through
a wall that blocks LoS. When you count range to your target, you must also check if you have clear line of sight (LoS). Draw an imaginary straight line from the center of your creature’s zone to the center of the target’s zone. LoS is blocked if the line crosses through a zone border that has a wall on it with the blocks LoS trait. Walls do not normally block LoS if the line crosses diagonally through the corner of a wall border, as long as at least one side of that corner does not block LoS