Bertha, the world's largest tunneling machine, churning through the rock and mud beneath Seattle, has hit a mysterious roadblock—so mysterious, it is only known for now as "the object."
The New York Times reports that the machine—300 feet long and 5 stories tall—has ground to a halt. Built precisely not to be stopped by, well, just about anything, Bertha has apparently met her match. But what exactly is it? "Something unknown, engineers say—and all the more intriguing to many residents for being unknown—has blocked the progress of the biggest-diameter tunnel-boring machine in use on the planet," the NYT writes.