I have yet to find a bath in a "public bathroom". Where is it hidden?

There is an exhibit currently on at the Tate Britain art gallery. It is out in the street out front of the gallery and from the outside it looks like a box with mirrors making up all four walls plus the roof.

Inside there is a fully plumbed in toilet. However, the mirrors are one-way glass so from inside you can see out, but from the outside you can't see in.

Apparently it's quite liberating, if not a little unnerving to sit there and evacuate while being able to see the whole world go by.

And in a bar in NY the loo doors appear to be plain glass until you lock them, at which point they mist up. The doors are masive lcd panels that cost $20k each - but they are pretty impressive.