The completely vacant 14-story building is approximately 3 million square feet. It was built in 1932 and has been vacant since 1995.
The U.S. Postal Service no longer wants to wait for an appropriate buyer. They have decided to auction it off.
"It's time to let it move on and give somebody else an opportunity to see if they can make something excellent happen here," said Mark Reynolds, post office spokesperson.
The public auction, handled by Rick Levine and Associates, will take place on August 27. The suggested opening bid is $300,000.
"We are selling this building absolute, regardless of price, no matter how low. We've gotten a lot of inquiries from here in Chicagoland and the uses have run the gamut from something like...condos to office space to a casino to a hotel," said Rick Levine.
The post office served as an air raid shelter during the Cold War. Experts say much of the work in the lobby would be impossible to replicate. The new owner will have to keep the lobby since it is a landmark.
ABC7 got a tour of the space on Wednesday. Each floor is about 165,000 square feet. Each floor has spy stations.
A huge vault made of steel is in the lobby of the building. The door will be going to the Smithsonian Museum in Washington D.C.
"You could put a different town on each floor if you really wanted to," said George Kopes, building facility manager.
Kopes said it costs $700,000 a year to maintain. He said he would like to see someone purchase it and put it to great use.