There are a couple of dry-stone railroad bridges that have to be seen to be believed. Another link to them is here.
I second the idea of a visit to Williamstown. Don't miss the Clark Institute if you like museums. Great place and it's free.
Shelburne Falls is worth a visit if you have a chance. The glacial potholes and the Bridge of Flowers are pretty photogenic and the town offers a nice place for an artsy afternoon stop. Lampson and Goodnow cutlery is there (good outlet shop for kitchenware) and there is a hot-shop for blown glass.