From one of my favorite blogs, Nag on the Lake, a post about how workers in Tokyo moved section of train line underground in the course of an evening in 2013.
When the Shibuya Station Toyoko Line above-ground train shut down for good it was replaced with a new section of subway track connecting Shibuya Station and the nearby Daikanyama Station. The conversion of the line from above-ground to underground required 1,200 engineers and countless man-hours.
But this mammoth construction was virtually unnoticeable, because it all occurred during the train line's off-hours… over the course of one single night.
Image: Youtube screenshot