I'm pretty sure that every single tourist who goes to Venice takes a picture of the "bridge of sighs." The bridge is so named because it links the courthouse (on the left) with the prison (on the right). As prisoners walked the bridge from the courthouse to the prison, they would ... "sigh".
I've not done many black and whites, but this image seemed ideal for it. The original is below, followed by my B/W attempt. You'll notice that I cloned out the nearest boat.
Initially, I thought the first was selective coloring. The second I think is a little over-processed for what I had imagined. To me there is virtually no depth because of the tone mapping that looks like you used. Of course it is your vision and may be exactly the look you were after. Good work cloning out the boat!
I would tend to agree here about the image looking harshly over processed. Otherwise the image has great composition, so perhaps after another try at processing the B&W it will look as good on screen as this might look in print.