Perhaps because winters can be brutal, Chicagoans take their summers 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 you prefer your activity in the water or on dry ground, you'll probably find it here. For information, contact the city's park district (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), a free monthly publication available at many retail shops, grocery stores, 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 best known is Oak Street Beach. Its location, 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, one big hill that's great for kite flying, and even a small bait shop where anglers can go before heading to 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 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 the off season, all beaches are fair game for dogs. The police won't hassle you, I promise.)

Beaches officially open with a full retinue of lifeguards on duty around June 20, though swimmers can wade into the chilly water from 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 do anything stupid such as dive 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 people-watching potential, head north (through the crowds). After you pass Belmont Harbor, the traffic lets up a bit. Ride all the way to Hollywood Beach (where the lakefront trail ends) for a good but not exhausting workout.

To rent bikes, try Bike Chicago, which has locations at Navy Pier (tel. 312/595-9600), North Avenue Beach (tel. 773/327-2706), and Millennium Park (tel. 888/BIKE-WAY). Open from 8am to 8pm May through October (weather permitting), Bike Chicago stocks mountain and touring bikes, kids' bikes, strollers, and -- most fun of all -- quadcycles, which are four-wheel contraptions equipped with a steering wheel and canopy that can accommodate four or five people. Rates for bikes start at $8.75 an hour, $34 a day, with helmets, pads, and locks included. If you'd like to cycle your way past some Chicago landmarks, guided tours are also available.

Both the park district (tel. 312/742-PLAY) and the Chicagoland Bicycle Federation (tel. 312/42-PEDAL) offer free maps that detail popular biking routes. The latter, which is the preeminent organization for cyclists in Chicago, sells a much larger, more extensive map ($6.95) that shows routes within a seven-county area. The federation sponsors a number of bike rides throughout the year, including the highly enjoyable Boulevard Lakefront Tour, held in mid-September, 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, an avid cyclist, has tirelessly promoted the addition of designated bike lanes along many main thoroughfares, but 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.

Golfing

For a major metropolis, Chicago has an impressive number of golf options within the city limits (not to mention many plush and pricey suburban courses). The closest you'll get to golfing downtown is The Green at Grant Park (tel. 312/642-7888), an 18-hole putting course on Monroe Street between Columbus Avenue and Lake Shore Drive, just east of Millennium Park. It's not exactly tournament-level play, but it's more challenging than miniature golf -- and the setting can't be beat. The course is open daily from 10am to 10pm, and putters and golf balls are provided. Rates are $9 per round for adults, $6 for children under 13.

To warm up your swing, head to the Diversey Driving Range, 141 W. Diversey Pkwy. (tel. 312/742-7929), in Lincoln Park just north of Diversey Harbor. This two-level range attracts all levels -- from show-off heavy hitters to beginners -- and is very popular on weekends with young singles who live in the surrounding apartment buildings. The price is right ($11 for a bucket of 100 balls), and the setting is pretty much perfect.

The Chicago Park District runs six golf courses in the city. One of the most popular is the 9-hole Sydney Marovitz Course, 3600 N. Lake Shore Dr. (at Waveland Ave.), which many Chicagoans simply call Waveland. Thanks to its picturesque lakefront location, it's always full on weekends, so make a reservation well in advance (and don't expect a quick game -- this is where beginners come to practice). Another good bet -- and usually less crowded -- is the 18-hole course in Jackson Park on the South Side (63rd St. and Stoney Island Ave.). These city-run courses are open from mid-April through November; for information on greens fees, location, and hours, call the Chicago Park District golf office (tel. 312/245-0909).

For information about suburban golf courses, visit the website of the Chicago District Golf Association.

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 pretty much perfect: You're skating in the shadows of grand skyscrapers and within view of the lake. The rink is open daily from 10am to 10pm November through March. Admission is free, and skate rentals are $7.

The park district runs dozens of other skating surfaces throughout the city, 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. Rentals generally include helmets and pads. Bike Chicago, with locations at Navy Pier (tel. 312/595-9600), North Avenue Beach (tel. 773/327-2706), and Millennium Park (tel. 888/BIKE-WAY), charges $8.75 an hour or $34 a day (8am-8pm). Londo Mondo, 1100 N. Dearborn St. (tel. 312/751-2794), on the Gold Coast, rents 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, so go on, get out there. Chicago Sailing, in Belmont Harbor (tel. 773/871-SAIL), rents J-22 and J-30 boats from 9am to sunset, weather permitting, May through October. A J-22, which holds four or five adults, rents for $45 to $65 an hour; a J-30, which accommodates up to 10 people, costs $80 to $100 per hour. If you want to take the boat out without a skipper, you need to demonstrate your skills first (for an additional $15 fee). If you'd rather sit back and relax, you can charter a boat. Reservations are recommended.

Swimming

The Chicago Park District maintains about 30 indoor pools for lap swimming and general splashing around, but none is 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, slightly northwest of Navy Pier. The Chicago Triathlon Club marks a course here each summer with a buoy at both the quarter- and half-mile distances. 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).

Windsurfing

Chicago's gusty breezes are welcomed by those windsurfing along the waves of Lake Michigan. This isn't the place for beginners, though: If you decide to give it a try, sign up for private lessons with Windward Sports, 3317 N. Clark St. (tel. 773/472-6868). Classes ($50/hr.) are offered on weekends from May through August and usually fill up, so call for reservations as far in advance as possible.