[Shadow Stranger]

In FRUA you could hack underwater combat into a design but all combat would have to be underwater, as the hacks would apply in every combat.
You can have something triggered by arriving on the square that lies on the other side of a wall. But you could arrive on that destination square from as many as four other departure squares. Thus there is no guarantee that you arrived on a destination square by walking through a wall. You really do need a wall event, especially if a type of wall always calls the same event.
Edit:
If DC has a facing direction event, unlike FRUA, that could avoid the problem with four possible squares leading to the departure square. But it is simpler if the wall contains the event rather than having to manually place each event. Recreating the Tower of Flame from DQK would be a minor hassle.