This is an old installation piece in London by artist Monica Bonvicini called 'Don't Miss A Sec'.
It featuring a public restroom in the middle of a busy sidewalk that's constructed entirely of 1-way mirrors. That way the shitter (shittee?) inside can watch all the pedestrians go by while they strain and groan and shift their weight back and forth from one buttcheek to the other hoping that'll get the mud flowing.
Public Toilet On The Street Made Of One Way Mirrors