I went to Asian Arts Museum of San Francisco, almost by accident, and caught the tail of "Drama and Desire": an exhibition of old Japanese paintings about the Pleasure Quarters of Edo. Tomorrow, Sunday May 4, is the last day it's running.
They included old shunga scrolls from 1700s. My eyes, I cannot unsee. Thank heavens, hentai made some good progress over the last 300 years.
BTW, those people did not bother to undress for sex, apparently.