Elon Musk's Boring Company spent years pitching cities on a novel solution to traffic, an underground transportation system to whisk passengers through tunnels in electric vehicles. Proposals in Illinois and California fizzled after officials and the public began scrutinizing details of the plans and seeking environmental reviews. But in Las Vegas, the tunneling company is building Musk's vision beneath the city's urban core thanks to an unlikely partner: the tourism marketing organization best known for selling the image that "What Happens Here, Stays Here."