At a restaurant in Prague, summer 1994.
First of all, you had to pay to use it. It was in a windowless basement of the restaurant. You gave your 10 kopeks, or whatever it was, to a large indolent woman with a mustache. She, in turn, handed you two squares of toilet paper (which had the consistency of pages from old Spider-Man comic books *), and let you proceed into the actual bathroom.
The toilet had no seat (because it'd undoubtedly been stolen to sell on the black market). The bathroom itself likely had not been cleaned that decade. And, previous occupants of the bathroom had left behind such an amazingly strong aroma of B.O. that there were actual visible stink-rays radiating through the air.
* - Before the trip, we had been warned about the amazingly awful Czech toilet paper, and thus had brought a supply of pocket-packs of Kleenex, for just such an emergency.