Partack
I'm not so sure that is an extra dwelling, that alleyway is the access to various garages and back-entrances to the residential areas above the shops. As you can see in the back-side photo, there's a shutter on the side building which appears to be a storage lockup/shed.

Attached photo(s):
https://westnordost.de/p/192931.jpg
https://westnordost.de/p/192932.jpg