Everything is tricky to find in Venice. Get off at Rialto and walk up the road asking side the supermarket. You will hit the square - take the middle lane next to H&M. It is then the second lane on the right. And then a little lane on your right with a big door at the end.
There is a timer light just inside the door- I was unaware of this and it is very dark.
There are three flights of stairs to get to the rooms so hydrate well before you get there. I had a corona back in the square.
I had room 9, own bathroom and terrace. Felt very safe and welcomed staying on my own but carting my case up the stairs nearly killed me and I'm reasonable fit. It is not modern just very comfortable.
I would stay there again, no problem.