Bertha, the world's biggest tunneling machine, is a five-story-tall monstrosity of drilling tasked with digging out the tunnel for State Route 99 to replace the Alaskan Way Viaduct. 

It's journey to the center of the earth underneath downtown Seattle began in July 2013, and since then the project has seen its fair share of successes and failures.

Follow the progress of the $3 billion megaproject with KUOW.