Which ultra wide angle lens for Venice (or do I actually need one)?

Thank you very much to everyone for all your replies - I really appreciate the time and effort you spent helping me.

What I discovered reading some of the replies is that my understanding of what a UWA lens does was actually incorrect.

I thought it would be perfect in getting more of the scene in the picture, whilst standing far away like I normally do. If I'm right in what I think you meant, a UWA lens is meant for taking photos whilst standingnearer to the subject, to give a different (somewhat 3D) perspective.

UWA lenses are not cheap. I'm in the UK and most of them are around £500 - £650. I would love to get one, just to allow me to take different types of pictures. However, I don't know just how much I would actually use it. I have a feeling my 16-85 would still command 90% of the time on my D90.

I have a feeling I will probably stick with my 16-85 and hope that the 16mm end can capture some nice images.

Another thing I could do is pop along to a camera store and take some pics with the various wide angle lenses in stock, and then view them on my computer.