a very mysterious door

i know a lot of you like mysterious doors. my colleague harry pointed this out to me. i can see it from my desk out the window (why DO they put my desk out the window).
i’ve never seen anyone open it. perhaps i need a brick door webcam ?
ntoe the curving distortion of the bricks in this picture. hoorah for converging verticals (and horizontals). they used to be so uncool you know.
by request (via comments) here is a close up of the signage which only adds to the mystery: