which he unveiled Wednesday night at a splashy event in Hawthorne, California, wasn’t a reusable rocket like the ones he’s building at his nearby SpaceX headquarters. Nor is it an electric vehicle, like the Teslas he is producing at a factory in Fremont, California.

Tonight, Musk showed off a 1.14-mile test tunnel — that snakes its way underneath 120th Street in the city of Hawthorne — that his other business, the Boring Company, dug for about $10 million using a modified boring machine called Godot. (That $10 million figures includes the cost of building the tunnel, all internal infrastructure, lighting, 
communication and video, safety systems, ventilation, and track, according to the company.) For Musk, this is merely a demonstration of what could be: a network of low-cost tunnels used for transportation, utilities or water and built for millions of dollars, or even billions less than those constructed for subways or trains.

And it’s a vision that he’s funding, for now. Musk estimates he’s spent about $40 million of his own money funding The Boring Company