The Descent: Journeys in the Dark (Second Edition) Wiki

Line of sight is a method to check the possibility to attack a figure, enemy, token, obstacle, etc. A figure may only target a space in his line of sight.

In order for a figure to have line of sight to a space, a player must be able to trace an uninterrupted, straight line from any corner of that figure’s space to any corner of the target space.

If the line passes through the edge of a map tile, a door, or a blocked space (a space containing a figure or obstacle), the target space is not in line of sight.

If the line passes along the edge of a blocked, the target space is not in line of sight. However, if the line only touches the corner of a blocked space (without passing through the space itself), the target space is in line of sight.

Since adjacent spaces always share at least one common edge or corner, there is no need to trace line of sight between adjacent spaces. A space adjacent to a figure is in line of sight.