IN a city of superlatives, that once upon a time boasted the world's busiest airport, the world's first and biggest Ferris wheel, the world's greatest quarterback, the USA's most efficient post office (so they claim) and three of the world's tallest buildings, no superlative, it seems, is too grandiose for Chicago.

In the home of the world's original skyscraper, work has already started on another statement structure that, which when built, will trump The Trump (Donald's new riverside hotel and condominium), sore above the Sears, pull the flush on the John (Hancock that is) and really put the super into superlative by laying claim to the world's tallest residential building and the tallest building in the western world designed by a worldfamous architect.

The Chicago Spire, located on a 2.2-acre site on the shores of Lake Michigan, designed by Spanish engineer, sculptor and starchitect Santiago Calatrava and developed by Irish property entrepreneur Garrett Kelleher, executive chairman of Shelbourne Development, is a jaw-dropping, neck-aching 150-storey, seven-sided glass tower that twists and turns up to pierce the sky 2,000ft above a public plaza below.

And unlike other super structures that have commercial units at its base, this one is wholly residential, boasting 1,193 residences with a private viewing tower at its summit.

Kelleher, who paid $64m for the site, and donated a further $9.6m to revamp neighbouring duSable Park, started work on the building in June. When complete in 2011, it will have cost $2bn, $300m of which he will fund himself, though the project is also being backed by Anglo Irish Bank.

Officially launched to an audience of 500 invited movers and shakers last Wednesday at a glitzy event in downtown Chicago, fans of the Spire hailed it as the most iconic building of the 21st century.

Critics, however, slammed its design, calling it the world's most terrifying dentist's drill and questioned its need in a city that already has more than its fair share of iconic buildings.

Also under scrutiny was its launch timing. Falling prices and rising interest rates in an unstable US market could see the Spire pulled back down to earth. Fuelling further criticism is the fact that Kelleher postponed preconstruction sales until January 2008, citing difficulties with paperwork.

It is estimated that over 13,000 new downtown condos are due for completion in Chicago from now until 2010, so Kelleher has a lot of competition if he's expecting 65% of the units to be filled by Chicagoans. But just who they are and where they're getting their money from is anyone's guess.

Still, while sales at Trump's 92-storey tower are reported to be sluggish, to date the Spire has had over 4,000 enquires from the US, Europe and even as far afield as Kazakhsthan.

And while there are some, including Trump, who doubt that the Spire will ever be built, Kelleher is convinced of its success, which he attributes solely to the fact that this is a truly amazing building. Failure is not an option for this man.

"The downturn in the US property market will not impact on sales at the Spire at all. The sub-prime problem is a middle market problem.

This is a high-end luxury project. And the fact that it's been designed by Calatrava, a modern day Leonardo da Vinci of architecture, makes it truly special and highly desirable. It's an iconic building and people will want to live in an iconic building, " he said at the launch.

Whether it's a soaring sales success that will net its owners excellent appreciation or high rental yields, it seems this is not really the issue here. This is a building that will truly put Chicago on the world map. It's France's Eiffel Tower, New York's Empire State Building and Dubai's Burj. On the whole, Chicagoans are really proud of it.

Who wouldn't want to live in a condo in the sky? For the high flyer, this really is living the high life . . . literally. Hey, if you can't stand the height get out of the city.

Units are all completely individual and range in size from 49.61sq m (534sq ft) to 956.25sq m (10,293sq ft), with prices from $750,000 for the smallest suite soaring to a dizzying $40m for a master penthouse on the 142nd floor.

All boast 10ft-tall ceilings and walls of glazing with unimpeded and unparalleled views of the city and river. And every little detail has been meticulously thought out, right down to the design of the door handles.

Buyers can also choose from 28 Calatrava signature 'gallery' units which feature a custom-designed circular bed enclosure with sliding glass doors, sleek, streamlined handless floor-to-ceiling storage units, designer touch control kitchen and spa-like, marble-clad bathroom.

Among its many engineering achievements, the Spire will have the world's longest elevator run at 1,864ft.

It will also have good green credentials. Recycled rainwater will be used to treat the landscaping, riverwater will be reused for cooling and waste storage will be recycled.

More importantly, the glass used in its construction is bird-friendly so there's no fear of feathered friends crashing and dying against its windows.

Amenities at the Spire, located on the first nine floors, are exclusive to residents and seriously impressive and will include a residents' library, children's game area, private cinema, private dining room, ringshaped recreational and lap pool, cigar room, and business centre with conference room.

Whatever the views and opinions on the Spire, and there will be many over the next four years, there's no denying the windy city just got mighty prettier. Bah humbug to the begrudgers.

Further information from www. thechicago spire. com or contact Savills HOK, which will be handling sales