There's a couple of options for working out and sports on campus. Paying the athletic fee gives you right to a locker and use of swimming pools and some installations, but check schedules first because the athletic department clearly prioritizes use of anything by the varsity teams. If you want to work out and can do without a locker you may want instead to buy one of the various plans to use the Body Shop. These are gyms with Nautilus machines, a few free weights, and various aerobic machines (treadmills, stairmistresses, nordictrack ski machines, etc.); you pay per visit or per semester. Totman Gym (diagonally across the LGRC) has one in the basement, and you can use Totman's showers et al. without paying the athletic fee (about $35/semester) if you don't need a locker. To use the Mullins installations (racquetball and ice-skating) you must pay a different fee (!) but it's not high (maybe $10/semester).
The Amherst Leisure Services offers a number of activities and courses; they also organize soccer, volleyball, and other leagues. You can take classes on how to fix your bicycle, on American Sign Language, yoga, dance, etc. (check their quarterly guide of activities).
Hiking trails of different lengths and difficulty crisscross the area. The Notch visitor center (on Rt. 116 in South Amherst) is a good starting point, but there are trails closer to downtown Amherst; ask. The UMass Outing Club leads organized hikes, camping trips and other excursions and even rents equipment.Information about nearby state parks and forests is available from the Massachusetts Department of Environmental Management . Also see: AmherstCommon.com's outdoor recreation pages , Appalachian Mountain Club (Berkshire Chapter), Dayhiker's Guide to Northampton. If you go on hikes into remote areas, be aware that there is some hunting for a few weeks of the year. Again, ask! In the early Fall you can go hiking to see New England's famous foliage colors. Colors peak at slightly different times each year and in each region; for up-to-date information call the following numbers. Connecticut: 800-282-6863; Maine: 800-533-9595; Massachusetts: 800-447-6277; New Hampshire: 800-386-4664; Rhode Island: 800-556-2484; Vermont: 802-828-3236.
With miles of winding roads and mountain-biking trails, the area is a great place for bicycling at all levels of difficulty. For an easy, flat ride that is free of cars, try the bike trail that connects Amherst and Northampton. (Entrance on Route 116 just south of Amherst College.) For more extensive exploration, Valley Bicycle sells a bicycling map of Western Massachusetts that shows virtually every road and rates them according to traffic level and difficulty (slope). Other useful links: MassBike Online (Pioneer Valley Chapter), Franklin-Hampshire Freewheelers.
In the winter you can ski cross-country (nordic) on various trails in Amherst or go to Northfield or places farther away. With the closing of Mt. Tom for skiing, you have to travel a bit farther for downhill (alpine). You can drive between two and four hours to very good ski places in the Berkshires, Vermont and New Hampshire. Check out Gorp.com for more info.