For most visitors, Western Mass . means the Berkshires, where most of the region’s cultural attractions can be found. The southern Berkshires  are focused more on performances and shopping, while the northern mountains  have art museums and outdoor pursuits. If you have more than a few days to spend, it’s well worth spending time in the Pioneer Valley  as well, where the college towns of Amherst  and Northampton  perfectly blend big-city culture with small-town charm.
Ideally, a visit to this area in its entirety would last about a week. That kind of time provides two to three days to explore the antiques stores, theater, and arts of the Southern towns; approximately three days to take in art exhibits, galleries, and to hike several of the trails in the mountains; and two more days to soak up the funky culture of the Pioneer Valley’s  coffee houses and shops around campuses like Smith and Amherst Colleges.
The best time to see the entire region is in autumn, so that you can take in brilliant foliage at nearly every turn. If you visit during the summer, however, plan to spend at least an extra day or two in the Berkshires, where the ongoing outdoor concerts at Tanglewood  and summer theater festivals could keep you happily busy for weeks.
The area is a year-round destination, with hotels, restaurants, and attractions staying open throughout the seasons. Note, though, that many restaurants do not offer all meals; many higher-end spots serve lunch and dinner (and sometimes dinner) only. Always call ahead to be safe.