I think it was because the clue tells them to find a museum, and I think the girls were probably looking for something that, in their mind, fit the description of "a museum".
I mean, looking at this place, it just seems like a warehouse/storage facility. If you're rushing/tired/not paying attention, one could presume that it's "not a museum" and keep going past it.
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So I could buy in to the idea that they were in the area, looking, but not REALLY looking. A slight inattention to detail that cost them a lot of time, and ultimately led to their elimination.