step 2.

what is the exact probability that it didn't fall in there?

or, that the rain wasn't falling and I didn't take a tram instead? (I would have taken a 22)

or that these guys didn't happen to arrive before me.

(this picture was taken on a Friday, and I had found it on a Thursday.)

A hypothesis: The owner used the ATM machine and after/before accidentally dropped his/her wallet.

And that one is a 'leather butique'

now it's closed but it might worth a try to check, maybe the wallet is actually from there!

I also found this on one of the nearby walls,

I have no idea what does it mean

it disappeared after a month or so.

preface