WHEN it comes to buildings, Chicago has other cities beat. Even Manhattan can't compete: not just with the number of soaring skyscrapers that stud the city's skyline but also the quality of the architecture. Chicago is an open-air classroom with some of the world's most remarkable modern buildings.
There are the Gothic-style decorations of the Tribune Tower, the base of which is studded with stones from some of the world's most significant structures; from the Egyptian pyramids and the Great Wall of China to the Taj Mahal, Abraham Lincoln's tomb and even the Berlin Wall. There's the sci-fi appeal of the Lake Point Tower, which is sinuous, black and curvy in a way that buildings usually aren't, and there's the two Marina City towers, which look like giant concrete corn cobs.
Any walk through downtown Chicago becomes a lesson in how to build memorable buildings. However, to know the stories behind the buildings and to understand why Chicago has such an amazing cityscape, sign up for one of the walking tours offered by the non-profit Chicago Architecture Foundation (CAF). It runs 85 themed tours covering different parts of the city, not just on foot but also by bike, Segway and bus.
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The Historic Downtown tour takes you back to where it all began. As a city, Chicago was something of a late bloomer, only starting to become a large centre in the 1860s. However, it grew quickly. When a fire devastated the city in 1871, destroying about 10 square kilometres of its centre, Chicago was full of rich men wanting buildings that demonstrated their power and prestige.
By happy coincidence, newly developed technologies such as steel-frame construction, lifts and electric lighting meant that buildings could now be higher than ever before. Chicago entrepreneurs competed to have the grandest buildings in town, many of which are still standing.
While the dark facades look heavy compared with today's glass-fronted designs, their grand lobbies are still dazzling. In the Marquette Building, completed in 1895 and named after the first European to explore the Great Lakes area, the double-height lobby features glittering mosaics by Louis Comfort Tiffany. Using mother-of-pearl and semi-precious stones, they depict incidents in Marquette's journeys. Bronze busts above the lifts depict Indian chiefs and expedition members, while panther heads decorate the revolving doors. Not far away, the architects of The Rookery, completed in 1888, hired a young architectural assistant to add to the light-filled, glass-roofed white-marble atrium. The beautiful decorations - including elegantly sweeping staircases enlivened with railings decorated with flowers - were an early success for Frank Lloyd Wright, who went on to create a number of other buildings in the Windy City.
Some of these can be seen on the CAF's Highlights by Bus tour, which gives visitors the chance to explore the architectural highlights that lie beyond the downtown area. Among them is another Wright design, the Robie House.
The tour includes a walk-through of this Prairie-style residence and an explanation of Wright's trademark features, including the low-slung design, the low-ceiling lobby (designed to make you move through into the main part of the house) and the custom-designed carpets and furniture.
Perhaps the highlight of the tour is a visit to the Illinois Institute of Technology (IIT), which is home to an impressive collection of buildings by Ludwig Mies van der Rohe, the modernist architect who, more than anyone else, helped shape Chicago's 20th-century skyline. Van der Rohe designed a number of the city's iconic buildings, including the Chicago Federal Centre complex and Farnsworth House, but it was his influence over several generations of local architects that made modernism one of Chicago's signature styles. (The architectural firm Skidmore, Owings Merrill, founded in Chicago in 1936, so faithfully followed his precepts that Lloyd Wright dismissed them as ''the three blind Mies''.)
Van der Rohe spent two decades as head of the School of Architecture at IIT. One of the perks of the job was the chance to create the master plan and design buildings for the new campus. With buildings such as Crown Hall, Van der Rohe demonstrated that it was possible to use glass as a key building material, an innovation that changed the face of architecture.
IIT has continued its tradition of ground-breaking architecture, with the Helmut-Jahn designed State Street Village residence hall and Rem Koolhaas's innovative McCormick Tribune Campus Centre, which includes a sliding glass door with a mosaic portrait of Van der Rohe. (Each ''dot'' in the mosaic represents a student.)
If the mosaic appeals to your sense of humour, head back to the downtown area to see Spanish artist Jaume Plensa's playful Crown Fountain in Millennium Park. At each end of a shallow reflecting pool, two 15-metre glass towers project ever-changing video images of Chicago citizens. Every few minutes, water pours through an outlet in the screen, so the water appears to spout from their mouths.
The fountain is almost as popular as Millennium Park's key attraction: a sculpture by Anish Kapoor officially called the Cloud Gate but known to locals as ''the bean''. The pretzel-like sculpture is made of highly polished stainless-steel plates, which reflect Chicago's skyline and the clouds above.
If you're not much of a walker sign up for the river tour, which offers a fascinating perspective on Chicago's urban scene. From the Trump Tower to the new Aqua - the tallest building in the world designed by a woman, local architect Jeanne Gang - it's a great way to see buildings that lie away from the heart of town. One of the most impressive is the Merchandise Mart, a rather ornate art deco building that houses a dazzling array of furniture and homewares wholesalers and retailers.
According to legend, the Sultan of Brunei once spent $1.6 million at the Mart to furnish his entire palace, claiming it was the only place the job could be completed in a week.
However, that's not the most remarkable thing about the Merchandise Mart. When it opened in 1931 - as the wholesale centre for the Marshall Fields retail emporium - it was not just the largest store in the world but also the largest building. Within its 18-storey interior, crowned with a 25-storey central tower, 372,000 square metres of floor space were available.
While the river tour is fascinating, the great joy of the walking tours is that you never know what you'll discover around the next corner.
As we wander around town on the Modern Skycrapers tour, I spot an unusual building: triangular, sand-coloured and decorated with a series of narrow vertical slits.
I figure it's another of Chicago's outside-the-square office buildings. When I ask our guide, I'm informed that it's not an office building.
It is the Metropolitan Correctional Centre and those decorative slits are in fact cell windows: they're deliberately narrow, circumventing the need for bars. And if it seems unusual having a jail in the central business district - well, the fact that the exercise area is 27 storeys up, on the roof of the building, means there's no need to worry about jailbreaks. That's Chicago - where even the clink is a grand piece of design.
V Australia flies from Sydney to Los Angeles with formal connections available with Delta Airlines to Chicago. Fares start at about $1700 a person on the net. 13 82 87, www.vaustralia.com.au.
The Sofitel Water Tower is another of Chicago's eye-catching buildings: a glass wedge shooting into the sky. The design theme is continued in guest rooms, which feature reproductions of classic furniture such as Barcelona chairs by adopted home-town favourite, Mies van der Rohe. The hotel's convenient location, good service and reasonable rates - which start at about $US160 ($157) a night - make it a handy Chicago base. 20 East Chestnut St, Downtown, +1 312 324 4000, www.sofitel.com.
Chicago Architecture Foundation tours, caf.architecture.org.
Five of the Windy City's best
1. The Willis Tower
Better known as the Sears Tower, this elegantly designed edifice was the tallest building in the world for 25 years and remains one of the jewels of the Chicago skyline.
2. Trump Tower
Understated is not a word usually associated with The Donald, yet Trump Tower - completed in 2009 and one of the city's newest landmarks - is refined rather than gaudy.
3. The John Hancock Centre
Its dark facade, studded with a series of stacked Xs, makes a striking impact but the design of Big John (pictured), as locals call it, is about function rather than form. The Xs are part of the bracing that protects this 100-storey building from the violent winds whipping off Lake Michigan.
4. The Chicago Board of Trade
This art deco classic has had two extensions - in 1982 and 1997 - turning it into a potted history of Chicago architecture.
5. Reliance Building (Hotel Burnham)
One of Chicago's prettiest buildings, its lavishly decorated interior and exterior have been painstakingly restored to 1894-era splendour. Look inside to admire the marble, mahogany and wrought ironwork.