In the second Urban Design Challenge, a design team crafted a "search Engine" digital gathering spot at the now-vacant Civic Forum block.

In the presentation at the Imax Theatre on Thursday night, the team outlined a porous complex featuring a five-story building and a four-story tower connected by raised walkways.

There is also a second-story roof garden reached at one point by a wide staircase and a cut-through from 11th Street to the front door of the Chattanooga Public Library. Another direct access point goes from 10th street to the Tennessee American Water Company.

The outside design of the towers includes a colorful computer-like pixelated mesh as well as several brilliant large screen images.

Narrow retail space rings the lower floor of the towers, and there is a covered walkway in line with the adjacent EPB building - designed by one of the lead team members, architect Bob Franklin.

There is below-ground parking at the site that was once part of the railroad grid leading to the Union Station and later the location for car lots and a Greyhound bus station.

The design team said the site is meant as a gathering place and incubator for technology and think tank firms. It could be a hub for techies ranging from alternative energy firms to Internet-based companies.

Mr. Franklin said at first he was "a curmudgeon" about getting involved in the planning process, but after going through it he said such an idea-exchanging process involving team members from different disciplines is essential for a progressive development of the city's remaining under-utilized spaces.

Matt Brown said the success and vibrancy of Search Engine could help fill up empty office space in nearby tall buildings.

He said at some point the Water Company building might be replaced with a facility to provide housing for Search Engine workers.

John Clark, a developer, said the only such similar urban tech hub he could find is in Florida.

Other team members include Steve Hasse, Glen Craig, Kate Creason, Kelly Fitzgerald, Kerrick Johnson, Paul Rustand and Rob Taylor.

All Urban Design Challenge events are free and open to the public.

They are sponsored by the River City Company.

The Civic Forum block is bounded by 10th and 11th streets and Market and Broad streets.