Spend a Penny

While talking to a group of guests on the tour, one of the ladies was remembering an incident on one of her previous holidays. She was talking about something she had needed to do but she first had to go "spend a penny" before she could proceed. At this point I stopped her to ask what she meant by "spend a penny". She explained that many years ago, in order to use a public toilet in England, it was necessary to put a penny in a small box attached to the stall of the toilet. Thus, when Nature calls they say they have to "spend a penny".
And by the way, contrary to what you may be thinking, this anecdote did NOT come from Mrs."P"
I remember pay toilets in America but it was never a penny!