GEOFFREY BAER VO: The Rookery Building in the heart of Chicago's business district has a surprise inside.

On the outside, it's all heavy stone.

But after you enter, and pass the elevators, you emerge into a beautiful space so light and airy, you almost feel like you've gone back outdoors.

There are all sorts of reasons to make a place beautiful.

Here, at least part of the idea behind the beauty was the bottom line, according to Pulitzer Prize winning architecture critic, Blair Kamin.

- [Blair] When you have these big floors, you really need to bring natural light and air into the building in order to make it rentable, in order to make money.

In the mid-1880s, electric light and gas light were very primitive.

So that's the functional reason behind this space, but obviously, the original architects, Daniel Burnman and John Root, then later, Frank Lloyd Wright, elevated that functional need into something truly extraordinary.

- [Geoffrey] So above this ceiling is sort of a hollow space so that the interior offices get light.

- [Blair] Yeah, light and air.

- [Geoffrey] And air?

- [Blair] Don't forget air.

No air conditioning in those days.

You know, air conditioning doesn't really become a factor in office buildings until after World War II.

So if you wanna rent space and make money, you've gotta deal with those practical things.

I mean, art, artful architecture is nice, but the bottom line counts too.

- [Geoffrey] Yeah, well I think you're making a point there, that there's something very Chicago about the practicality behind all this beauty, right?

- [Blair] Yeah, absolutely.

I mean, that is the story of Chicago architecture, elevating the pragmatic into the artistic.

That's what Chicago architects are so skilled at doing.

- VO: For busy office workers who didn't want to wait for the primitive elevators, architects Burnham and Root elevated the utilitarian spiral stairway into a work of art.

The Rookery might have seemed beautiful in 1888, but less than 20 years after it opened, it was already looking dated.

Bad for business.

- [Blair] Originally, this is like a Victorian bird cage that John Root of Burnham and Root designed.

- VO: By 1905, tenants were looking for the next big thing, so the Rookery hired hotshot architect, Frank Lloyd Wright, to give the lobby a facelift.

- [Blair] You really see Wright's hand here, and the way he modernized the space while being respectful to Roots' original.

Wright added characteristic Wrightian touches.

Urns.

Brendan Gill, the critic, once accused Wright of Urnomania.

(Geoffrey laughs) - [Geoffrey] He loved urns.

- [Blair] He loved urns.

And he brings nature into the space on top of the urns, right?

So that's Wrightian.

But also, he uses the marble incised with gold, with the Arabic motif, to lighten and animate.

Wright is simplifying, and he's making it geometric, and it connects to the past, and yet it also anticipates the future.

Wright was brilliant.

And what he did elevated the space even further.

It made it, it accentuated its lightness, its airiness, its ethereal qualities, its contrast with the exterior.

It brought it into the 20th century, literally.