The first formalized bathing costume in the modern era was not a piece of clothing at all but a piece of architecture: a bathing machine. Invented by a Quaker in 1753, the horse-drawn half carriage contained a “modesty tunnel” that allowed a fully clothed Victorian woman to enter the sea privately.
~Lencek, Lena and Gideon Bosker. 1989. Making Waves: Swimsuits and the Undressing of America. San Francisco, CA: Chronicle Books.
I'll have photos soon.