A long sleeved dress and comfortable sandals is perfect for breezy, spring weather. It's not too casual, but it's not too dressed up either! I advise taking a crossbody bag of some kind so you don't have to hold stuff in your hands while walking around campus. It's also a good idea to wear a watch, because certain events during the tour might happen during certain times (and looking at your phone to check the time might be distracting).
If it's still cold where you're touring, wear comfortable yet appropriate clothing! I suggest a pair of dark wash jeans, a button down shirt, a cute vest, and comfortable flats. A Longchamp tote is the perfect size to hold your vest if you get hot while inside buildings!
If it feels like a sauna outside, I'd recommend wearing nice chino shorts and a flowy blouse to keep you cool! Again, make sure your sandals are comfortable, because you'll most likely be doing a lot of walking (and you really, really don't want to get blisters).
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