Italy Trip - Lens

My wife, my in-laws and I will be going to Italy in two weeks. I
have a basic Nikon D3000 DSLR with the stock lens (AF-S DX 18-55mm). Was
wondering if you had any suggestions in terms of a solid lens to buy
between now and the time we leave that would give me the flexibility of
taking group shots and also be able to capture the beauty of the
landscape/architecture. The lens I have now takes decent group photos but
takes mediocre landscape pictures.

Thanks a bunch!