For decades the 80-plus acre tract of land between the train tracks and Hopkins Avenue bustled with activity. As many as 10,000 workers for A. O. Smith from 1910 to 1997– and, from 1997 until 2006, Tower Automotive – worked there in dozens of buildings.

They built car frames, made pipes, hot water heaters, airplane propellers and vats for breweries, fabricated bomb casings during World War I and many other things over the years.

The City of Milwaukee bought the site east of the tracks in 2009, says Benjamin Timm, the City of Milwaukee Department of City Development's project manager for the 30th Street Industrial Corridor, of which the site is a part.

"The City was very concerned about what would happen with this because of the impact it would have on the North Side of Milwaukee," he says.

Now, a mere handful of buildings still stand and a couple of those – some small utility buildings – will likely have fallen between the time I write this and when you read it.

"We started doing structural assessment of the buildings, environmental assessment and ultimately cleanup and demolition of the buildings," says Timm.

"We originally looked at all the buildings out here to see if we could keep some standing. Basically, what's in good shape, what could stay and what could go. Ultimately this whole facility was meant to function as a single unit. So, it's very difficult to break these buildings apart and let them stand on their own, so we decided to tear everything down."

A dozen, maybe two, bulldozers and excavators are on the old Tower site east of the tracks working to ready it for future industrial development.

On the south end, in a long, building along Townsend Street, Spanish train manufacturer Talgo is finishing up some train sets destined for Oregon – one rode the rails out in early December and by mid-month another was parked out on a siding – before it finishes ramping down and closing. Two sets for Wisconsin are currently inside the building.

The 70-acre parcel of land west of the tracks that was long part of the A. O. Smith/Tower Automotive complex is divided up and controlled by various owners. The City of Milwaukee owns a large portion that serves as a Department of Public Works facility.

Two of the buildings still standing on the city's land to the east are the two-story 1910 A. O. Smith headquarters and adjacent to it, to the south, the 1930 Research & Engineering building, which offered a light-filled workspace for its 400 engineers.

By 1910, A. O. Smith, which started out as a bicycle manufacturer in Walker's Point, was making automobile frames for Henry Ford.

The two-story red brick 1910 building with its decorative gable and curly-cues flanking an engraved "A. O. Smith Co." nameplate above the entrance is being preserved. According to Benjamin Timm, the City's project manager for the 30th Street Industrial Complex, of which the site is a part, says there has been some interest from the private sector in this building.

There's almost nothing left of the original interior. A decorative railing runs up a staircase, a curved glass window wraps itself around a cut-off corner along a hallway. The one major exception is a first-floor corner conference room, with a fireplace, rich wood paneling and leaded glass windows that have been bordered up for protection.

Timm says estimates at rehabbing the building have run around $1 million.

Unfortunately, estimates for its seven-story neighbor run somewhere in the range of 30 to 50 times higher.

But, remember, this structure – designed by the Chicago firm of Holabird and Root – was not only the first multi-story building with full curtain walls of windows made of large plate glass in aluminum frames, but also the first to use extruded aluminum and was one of the first multi-story International Style buildings constructed in the United States.

Despite its disrepair – which is clear from the netting that's been attached to prevent falling shards when the windows burst outward (as has occurred) – the building is clearly a gem, with its beveled rows of windows running from ground to roof – six on the facade, eight on the south and north sides – flooding the interior with light.

But those gigantic windows aren't the only source of natural light in the u-shaped building. In the space created by the sides of the U is a giant open interior space that is two stories tall, with a grid of small windows serving as an arched skylight.

A giant overhead crane – one of hundreds that were on the site – running on rails was installed in this research and development lab space. It's still there, though it's dormant now. In the terrazzo floors in this giant space are rows of metal rings that helped add strength to the floors.

"It wasn't built with energy efficiency in mind," says Timm of the R&D building. "Lots of natural light, but it's basically metal and glass and that's the only thing separating the outside from the interior. Both metal and glass do a good job of conducting hot and cold."

We entered the building through a door in the back and so, we saved the first floor's biggest treat for last.

The lobby is perhaps the most beautiful art deco space in the city. Aluminum art deco sections share wall space with glossy emerald panels and matching aluminum doors in the lobby, which isn't huge. Walking into the lobby, with its terrazzo floor that includes a multicolor decoration punctuated by translucent areas once lit from below, feels like stepping into a long-lost work of art.

Should this building ever be demolished, I hope someone has the foresight and the ability to remove the lobby piece by piece and reconstruct it elsewhere. It is that gorgeous.

Off the lobby is a large conference room. Wood paneled, it looks like a set for television's "Mad Men." Almost hidden in the wall is a door to the men's room.

Upstairs, in what was office space, the areas are large, with those giant windows – each one a single pane of quarter-inch glass 9 feet wide by 13 feet tall – along the exterior walls. Some floors are in better shape than others.

On one floor it almost looks as though folks moved out last month. On that one, a discarded little Christmas tree lays on its side on the floor, still wearing decorations. On another, it feels like the '80s with walls that alternate between pink and turquoise.

As you ascend to the higher floors, the lack of heating and cooling systems (they were located in a now-demolished adjacent building) has taken its toll and the parquet floors are buckling, creating long strips of elevated flooring, poked up in an upside-down V shape.

In a small office, there are boxes and boxes of discarded files, still on the shelves. A membership booklet for an industrial union sits on a desk. Outside an office on another floor is an old issue of Penthouse magazine.

We climbed to the roof – passing through an HVAC space as quickly as possible because there's still friable asbestos in there – and were treated to some great views. Everything on this side of town is low enough that you can see distant landmarks in every direction. To the southwest, Miller Park and Froedtert Hospital. Downtown to the southeast. Off to the northeast, there's Bayshore and far off on the horizon is Holy Hill.

To the northwest we can see the two glass office towers near Good Hope Road and Highway 45. That's where A. O. Smith's headquarters are now located.

We also get a great view of the entire Tower Automotive site from up here. It's amazing to see how the site's many buildings – most of which had been built into and on top of one another; some were connected by above-ground passages, others by tunnels (workers uncovered all kinds of underground bomb shelters, torpedo factories and the like) – have been cleared.

The City has completed a lot of work on the site and is working now on moving into the future with its master plan.

"We're going to start a full-scale marketing initiative in 2013," says Timm. "When we started this project and people would drive down Hopkins all they'd see is a wall of buildings. You're telling them what you're doing, you can tell them your vision and they're standing there saying, 'you're crazy.'

"Now they can come and see 80 acres of open land, now people are starting to get it."