Lace Curtains
We all know why grandmom and grandpop had lace curtains... so they could spy on their neighbors, obviously. At first, they were a bit of a status symbol due to the price of fine lace, but once machine-made synthetics were introduced, lace curtains donned just about every window. Creep around your grandparents house, 99% sure you'll find at least one still lurking.