Millennium Park

Stand still on the Great Lawn for a moment. Beneath the grass, beneath your shoes, a commuter train may be rolling past right now. Everything around you, the lawn, the gardens, the silver band shell, sits on a huge deck built over railroad tracks and parking garages. You are standing on a roof.

This is Millennium Park, 24.5 acres at the northwest corner of Grant Park in downtown Chicago. Because of what lies underneath, it is often called one of the largest green roofs in the world. It is free, it is open daily, and since the day it opened it has been the city's favorite gathering place.

For more than a century, this block was an open trench of rail lines and gravel lots, a working scar between Michigan Avenue and the lake. In the late 1990s, the city decided to cap it with a park to mark the year 2000. The name stuck. The deadline did not. Millennium Park opened in July 2004, four years late, and its cost grew from 150 million dollars to about 475 million, with roughly 200 million of it raised from private donors. The jokes ended quickly. The crowds never did.

The park's centerpiece rises at the head of the lawn, the Jay Pritzker Pavilion, designed by the architect Frank Gehry. Ribbons of stainless steel curl and peel around the stage like petals. Overhead, a trellis of steel pipes arcs across the entire lawn. It carries the sound system, so a listener at the back hears the same balanced sound as someone in the front row. The pavilion seats 4,000 people, and the lawn holds 7,000 more.

Music here is free. The Grant Park Music Festival, a tradition dating back to 1935, plays free classical concerts through the summer. On concert evenings the lawn fills with blankets, picnic baskets, and the pop of corks. Few cities offer an orchestra under the open sky at no charge. This one has done it for generations.

A short walk toward Michigan Avenue brings you to Cloud Gate, the mirror-polished sculpture everyone calls the Bean. Anish Kapoor's drop of liquid steel reflects the skyline, the sky, and you. Give it time. The crowd around it is half the show.

At the park's southwest corner, two glass towers face each other across a shallow sheet of water. This is Crown Fountain, by the Spanish artist Jaume Plensa. The towers stand 50 feet tall, and their screens play slow video portraits of about a thousand Chicagoans, one face at a time. In summer, water pours from each mouth like a modern gargoyle, and children wait below, shrieking happily when it comes.

Behind a tall hedge east of the Bean hides Lurie Garden, a piece of prairie folded into downtown. The Dutch plant designer Piet Oudolf filled it with coneflowers, salvia, and grasses that shift color week by week. The plantings stand all winter, rattling and gold. The hedge that shelters them is a quiet joke, a big shoulder for the City of Big Shoulders.

From the lawn's east side, a walkway of brushed steel snakes up and over Columbus Drive. This is the BP Bridge, Frank Gehry's first bridge anywhere. Its curves hide the view, then open it, and its walls block the traffic noise below so the lawn stays quiet during concerts. It lands in Maggie Daley Park, with its climbing walls and playgrounds.

Winter changes the park rather than closing it. The McCormick Tribune Plaza becomes an ice rink, and skating is free if you bring your own skates. A giant Christmas tree goes up nearby, and the Bean wears a cap of snow. In summer, the lawn hosts movie nights, morning yoga, and festival after festival.

The park is free and typically open from early morning until late evening. Give it at least an hour. Most visitors come for the Bean and stay for whatever they find next, a rehearsal drifting from the pavilion, a wall of water, a garden humming with bees. And the Chicago Cultural Center across Michigan Avenue is worth a look for its glowing Tiffany glass dome.

Remember the trench this used to be. Smoke, tracks, and parked cars, in the middle of one of the great skylines on Earth. It took a stubborn decade and a fortune to put a roof over it and call the roof a park. Stand on the lawn once more before you go. If you feel a faint rumble underfoot, that is the old city, still running beneath the new one.