"It's just fascinating that you can stand in one place and see what's functioning on the entire machine," Scarfia said of the control room.

The tunnel itself is made up of rings, which are placed one at a time. Each ring is made up of eight concrete segments. Those segments weigh 25,000 pounds, and measure 14-feet long, 5-feet wide and 2-feet deep.

The construction crews plan on using 12,000 concrete segments.

Thrust cylinders propel the machine forward, and brushes leave grease to seal the edges of the concrete.

During an emergency, the 16 person crew takes refuge in a small bunker. Inside, communication devices give them access to the outside world to call for help.

It will take about two to three months for Harriet to come out of the tunnel. At that point, it will be turned around and start the westbound tunnel back to Miami.