Lens for my D80

[Wills]

Hi to all,
I have a Nikon D80 just this April and am using the kit lens 18-135mm. I don't have any problem with this lens. But since I am planning to visit Europe this next month, I am trying to buy a lens that would suit me to capture those beautiful monuments. I heard that I should go for Wide angle lenses, please suggest what would be the best lens that I can carry and get nice picture in and out of monuments?

Also, I would like to know if my existing lens would be sufficient and what should I change in some settings to get the wide angle pictures?

I really need your suggestions and opinions.

Thanks!