Thank you for all sharing all this information. I didn't think it would involve several, not all simple possible solutions. I've been looking at maps of the city and its layout.
Sorry I didn't make it clear. I don't really need to save money, though I'll be in Venice (Dorsoduro) for 22 days. I'm just really interested in the easiest way to get to Piazza Reale after a long plane trip Seattle - Frankfurt - Venice.
My landlady wrote to me via WhosApp or the plaform I rented through ways of getting to the apartment but I wasn't able to find the message. I had read through it but was still not very clear. I asked her again yesterday to send me directions but haven't heard from her yet. She had mentioned a water taxi (from where exactly?).
Previous guests/tenants had mentioned that she had met them somewhere. Addresses in Dorsoduro, apparently, do not have street numbers. I don't recall if she suggested meeting at Campo Santa Margherita.
I'd like to have a clear notion of how to get there way before I leave Seattle.