Perhaps because Chicago's winters can be so brutal, Chicagoans take their summers very seriously. In the warmer months, with the wide blue lake and the ample green parks, it's easy to think that the city is one big grown-up playground. Whether your fancy is watersports or land-based ones, you'll probably be able to find it here. The park district can be reached at tel. 312/742-PLAY; for questions about the 29 miles of beaches and parks along Lake Michigan, call the park district's lakefront region office at tel. 312/747-2474.

Another handy resource is Windy City Sports (tel. 312/421-1551; www.windycitysportsmag.com), a free monthly publication that you'll find at many retail shops, grocery stores, and bars and cafes.

Beaches

Public beaches line Lake Michigan all the way up north into the suburbs and Wisconsin, and southeast through Indiana and into Michigan. The most well known is Oak Street Beach, the location of which at the northern tip of the Magnificent Mile creates some interesting sights as sun worshippers sporting swimsuits and carting coolers make their way down Michigan Avenue. The most popular is North Avenue Beach, about 6 blocks farther north, which has developed into a volleyball hot spot and recently rebuilt its landmark steamship-shaped beach house and added a Venice Beach-style outdoor gym; this is where the Lincoln Park singles come to play, check each other out, and fly by on bikes and in-line skates. Hollywood-Ardmore Beach (officially Kathy Osterman Beach), at the northern end of Lake Shore Drive, is a lovely crescent that's less congested and has steadily become more popular with gays who've moved up the lakefront from the Belmont Rocks, a longtime hangout. For more seclusion, try Ohio Street Beach, an intimate sliver of sand in tiny Olive Park, just north of Navy Pier, which, incredibly enough, remains largely ignored despite its central location. If you have a car, head up to Montrose Beach, a beautiful unsung treasure about midway between North Avenue Beach and Hollywood-Ardmore Beach (with plenty of free parking). Long popular with the city's Hispanic community, it has an expanse of beach mostly uninterrupted by piers or jetties, and a huge adjacent park with soccer fields and one big hill great for kite flying -- even a small bait shop where anglers can go before heading for a nearby long pier designated for fishing.

If you've brought the pooch along, you might want to take him for a dip at the doggie beach south of Addison Street, at about Hawthorne and Lake Shore Drive -- although this minute spot aggravates some dog owners because it's situated in a harbor where the water is somewhat fouled by gas and oil from nearby boats. A tip: Try the south end of North Avenue Beach in early morning, before it opens to the public for the day. (Also consider that, in off-season, all beaches are fair game for dogs. The police won't hassle you, I promise.)

Beaches are officially open with a full retinue of lifeguards on duty beginning about June 20, though swimmers can wade into the chilly water Memorial Day to Labor Day. Only the bravest souls venture into the water before July, when the temperature creeps up enough to make swimming an attractive proposition. Please take note that the entire lakefront is not beach, and don't go doing anything stupid such as diving off the rocks.

Biking

Biking is a great way to see the city, particularly along the lakefront bike path that extends for more than 18 miles. The stretch between Navy Pier and North Avenue Beach gets extremely crowded in the summer (you're jostling for space with in-line skaters, joggers, and dawdling pedestrians). If you're looking to pick up some speed, I recommend biking south -- once you're past the Museum Campus, the trail is relatively wide open, and you can zip all the way to Hyde Park. If you want a more leisurely tour with good people-watching potential, head north (through the crowds) and be patient -- once you pass Belmont Harbor, the traffic lets up somewhat. Ride all the way to Hollywood Beach (where the lakefront trail ends) for a good, but not exhausting, workout.

To rent bikes, try Bike & Roll, which has locations at Navy Pier (tel. 312/595-9600) and North Avenue Beach (tel. 773/327-2706). Open from 8am to 10pm May through October (weather permitting), Bike & Roll stocks mountain and touring bikes, kids' bikes, strollers, and -- most fun of all -- quadcycles, which are four-wheeled contraptions equipped with a steering wheel and canopy that can accommodate four or five people. Rates for bikes are $9.75 an hour, $34 a day, with helmets, pads, and locks included. Quadcycles rent for $20 per hour. Both locations offer free lakefront bike tours daily; tours start at 1:30pm and run about 2 1/2 hours. There's a 15-person maximum per tour (and they usually fill up), so call in advance to make a reservation.

Both the park district (tel. 312/742-PLAY) and the Chicagoland Bicycle Federation (tel. 312/42-PEDAL; www.chibikefed.org) offer free maps that detail popular biking routes. The latter, which is the preeminent organization for cyclists in Chicago, also sells a much larger, more extensive map for $6.95 that shows routes within a seven-county area. They sponsor a number of bike rides throughout the year, including the highly enjoyable Boulevard Lakefront Tour, held in late June, which follows the historic circle of boulevards that had their genesis in the Chicago Plan of 1909. It starts in Hyde Park at the University of Chicago campus.

A word of caution: Never head anywhere on the city's streets without first strapping on a helmet. Chicago Mayor Richard M. Daley is an avid cyclist himself and has tirelessly promoted the addition of designated bike lanes along many main thoroughfares. But, that said, most cabbies and drivers tend to ignore them. Bike with extreme caution on city streets (you can get a ticket for biking on the sidewalk) and stick to the lakefront path if you're not an expert rider. Locking your bike anywhere you go is a no-brainer.

Ice Skating

The city's premier skating destination is the McCormick-Tribune Ice Rink at Millennium Park, 55 N. Michigan Ave. (tel. 312/742-5222). The location is unbeatable; you're skating in the shadows of grand skyscrapers and within view of the lake. The rink is open daily from 9am to 9pm November through March. Admission is free, and skate rentals are $5.

The park district runs dozens of other skating surfaces throughout the city, both along the lakefront and in neighborhood parks. Call tel. 312/742-PLAY for locations. There's also a relatively small rink at Navy Pier, 600 E. Grand Ave. (tel. 312/595-PIER).

In-Line Skating

The wheeled ones have been taking over Chicago's sidewalks, streets, and bike paths since the early 1990s. Numerous rental places have popped up, and several sporting-goods shops that sell in-line skates also rent them. The rentals generally include helmets and pads. Bike & Roll, with locations at Navy Pier (tel. 312/595-9600) and North Avenue Beach (tel. 773/327-2706), charges $9.75 an hour or $34 a day (you can have the skates 8am-10pm). A second spot is Londo Mondo, 1100 N. Dearborn St. (tel. 312/751-2794), on the Gold Coast, renting blades for $7 an hour or $20 a day.

The best route to skate is the lakefront trail that leads from Lincoln Park down to Oak Street Beach. Beware, though, that those same miles of trail are claimed by avid cyclists -- I've seen plenty of collisions between 'bladers and bikers. Approach Chicago lakefront traffic as carefully as you would a major expressway.

Sailing

It seems a shame just to sit on the beach and watch all those beautiful sailboats gliding across the lake. Go on, get out there. The Chicago Sailing Club, in Belmont Harbor (tel. 773/871-7245, www.chicagosailingclub.com), rents J-22 and J-30 boats from 9am to sunset, weather permitting, May through October. A J-22 holds four or five adults. Rates for a J-22 range from $35 to $55 an hour ($10 extra for a skipper). A J-30 accommodates up to 10 people and can sail at night. Rates are $70 to $90 per hour, plus $20 per hour for a skipper. If you want to take the boat out without a skipper, you need to demonstrate your skills first (for an additional $10 checkout fee). Reservations are recommended. Charters are also available.

Swimming

The Chicago Park District maintains about 30 indoor pools for lap swimming and general splashing around, but none are particularly convenient to downtown. The lakefront is open for swimming until 9:30pm Memorial Day to Labor Day in areas watched over by lifeguards (no swimming off the rocks, please). But be forewarned: The water is usually freezing. A good place for lake swimming is the water along the wall beginning at Ohio Street Beach, located slightly northwest of Navy Pier. The Chicago Triathlon Club marks a course here each summer with a buoy at both the 1/4- and 1/2-mile distance. This popular swimming route follows the shoreline in a straight line. The water is fairly shallow. For more information, call the park district's beach and pool office (tel. 312/742-PLAY).