Boulder or Sun Valley?

Neither town has a beach, so this comes down to what kind of summer swim you want. Boulder's options are close and easy: a small sandy area at the reservoir on the edge of town, and tubing down Boulder Creek through the middle of it.

Sun Valley's best swimming means a drive of about an hour to Redfish Lake below the Sawtooths. The setting is far more dramatic but the water stays cold all summer. Closer to town, the heated outdoor pools are the most dependable place to swim.

Boulder eats better and with more variety. It has seasonal Front Range cooking, unusually strong vegetarian choices, good bakeries and roasters, a Saturday market by the creek and a deep craft-beer scene. The hand-carved Dushanbe Teahouse makes a lunch you will remember, and Denver is close by when you want more range.

Ketchum does well for a resort its size, with après-ski grills and a few ambitious kitchens cooking trout, lamb and elk. Cheap meals are scarce, though, and some places close or cut their hours in spring and autumn.

Boulder has more to look at, though it still only fills a day. You can see the 1898 Chautauqua cottages and auditorium under the Flatirons, the sandstone and red-tile university campus, and I.M. Pei's atmospheric research laboratory on the mesa with its free weather exhibits.

Sun Valley's interest is mostly in its story. The railroad built it in 1936 as America's first destination ski resort, and the Lodge's corridors of film-star photographs recall that era. Hemingway's grave and memorial are in Ketchum. An afternoon covers it all.

Boulder offers a proper if early night out. There are taprooms, cocktail bars and pubs around Pearl Street, the student bars on University Hill are loud during term, and Denver is about 40 minutes away for clubs.

In Sun Valley, going out means après-ski: a few saloons, wine bars and hotel lounges in Ketchum, and sometimes a band on a busy winter weekend. Outside the ski season and midsummer, it is quiet by mid-evening.

Both are outstanding, and the difference is what you do outdoors. Boulder's trails start at the edge of town, with over 200km across the Flatirons, Green Mountain and Bear Peak. Eldorado Canyon is one of the country's great climbing walls, and cyclists come to train on the canyon roads. Rocky Mountain National Park's tundra and elk are about an hour away.

Sun Valley is built around a true ski mountain, Bald Mountain, with Nordic and backcountry skiing beside it. Summer brings singletrack biking and trout fishing on the Big Wood and Silver Creek, with the wilder Sawtooths and rafting on the Salmon River further north.

Boulder has far more within reach. An express bus runs to Denver's art museum, capitol and Union Station, and with a car you can visit Golden, Fort Collins and the Victorian mining towns of Georgetown and Idaho Springs.

From Sun Valley, most outings go into the mountains rather than to other towns. Hailey's small main street and the log-cabin outpost of Stanley are the nearest options, and Shoshone Falls is about two hours away. Boise is too far for a comfortable day.

Boulder fills a family's days more easily. Children can paddle in the creek, swim at the reservoir beach and walk the trails at Chautauqua, then watch the street performers on Pearl Street in the evening. The planetarium and the natural history museum cover wet afternoons, and Denver's zoo and aquarium are close.

Sun Valley is excellent for children learning to ski, with a separate gentle hill and a well-run school. In summer there are horse rides and an ice rink. Nothing is built just for children, though, and the midwinter cold is hard on toddlers.

Boulder is the easier place to manage without a car. The creek-side bike paths and underpasses link downtown, the campus and Chautauqua, and an express bus runs to Denver and on to its airport connections. You will still want a car for Eldorado Canyon and the national park.

In Sun Valley, a free bus links Ketchum, the village and the lift bases, so a ski week without driving is realistic. For anything else in the valley you need a car, the local airport is small, and the drive to larger airports can be snowy.

Boulder has more to browse. The brick-paved Pearl Street Mall has independent bookshops, galleries and toy shops, Twenty Ninth Street has the chain stores, and the climbing, running and cycling shops are excellent.

Ketchum's few blocks lean upmarket. There are fine and western art galleries with evening gallery walks, fly-fishing and ski shops, and boutiques selling cashmere and home decor to second-home owners.

Neither town is cheap, but Boulder is easier on the wallet. The trails cost nothing, the buses are reasonably priced, and staying in Denver and driving in is a simple way to save.

Sun Valley is pricier at every turn. Rooms, meals and lift access are priced for a wealthy second-home crowd, and there is very little budget lodging. Staying down the valley or visiting in the quiet shoulder months helps only so much.

Boulder has music all year. Small downtown rooms book touring rock, bluegrass and roots acts most nights. In summer the Colorado Music Festival plays in the wooden Chautauqua Auditorium and the Shakespeare festival performs outdoors on campus, and Red Rocks Amphitheatre is about 45 minutes away.

Sun Valley's season is short but charming. A professional orchestra gives free concerts in the pavilion by the lodge while people picnic on the lawn, and star skaters perform on the outdoor rink on summer evenings. Outside summer there is almost nothing.

Both are good places to slow down, but in different ways. Boulder's wellness is about the mind and body. Yoga and meditation studios are everywhere, there is a contemplative university, and massage and acupuncture are easy to find. Real soaking is scarce, with only a modest spring-fed pool at Eldorado Springs.

Sun Valley is better for warm water. It has full resort spas, outdoor heated pools that are lovely under falling snow, and rough natural hot springs by the creek up Warm Springs valley. It has no wellness culture, though, beyond quiet mornings and early nights.