Zephyrus points in the vague direction of what clearly is an open field.
Mizuki follows the direction of her finger, stepping closer to catch a good look of it. She squints and even extends her arm over the river but she feels nothing out of the ordinary, or anything that may suggest that she has come to the right place.
As good as a spell may be, in Mizuki's assumption, there must be some traces left behind—or any distinguishing factor that can allow her to determine that she has not stumbled into the wrong place.
"I don't think we are in the right place. We have to keep looking—" Mizuki insists, arguing with Zephyrus' persistent demand that the tower is definitely in front of them.
When she decides she won't be able to persuade the obstinate individual, Mizuki takes it upon herself to search the area as well, perhaps to look for any telling signs that could be of use to her.