Elon Musk's plans often sound like ideas that sit somewhere between genius and supervillain. 

The billionaire Tesla (TSLA) - Get Tesla Inc. Report CEO thinks incredibly big and that makes some of his ideas seem improbable at best. This man wants to build a city on Mars while revolutionizing transportation and energy on Earth.

Tesla has, of course, led the way in the move toward electric vehicles while also advancing solar power and battery technology. Musk's SpaceX has brought the internet to places it has never gone before, while it also works toward that eventual civilization on Mars.

Those efforts alone make Musk a visionary on par with anyone in history. But in addition to looking to the stars, the billionaire also sees the potential to solve another problem by going underground. 

His Boring Co. has invented a new way to dig tunnels more efficiently and at a lower cost than any other rival.

It's a company with a simple, but potentially hugely impactful mission:   

Boring Co. "creates safe, fast-to-dig, and low-cost transportation, utility, and freight tunnels The mission: solve traffic, enable rapid point-to-point transportation and transform cities," the company says on its website.

That's a bold idea that the company has been slowly putting into practice under one of the most-crowded, most-visited cities in the world.

Image source: J. Emilio Flores/Corbis via Getty

Boring Co. has slowly been building a tunnel system under Las Vegas. It started with a modest loop that connects the two halves of the Las Vegas Convention Center. That's more of a proof of concept than a viable use of the technology.

This first tunnel spans a little more than a mile, where drivers in Teslas shuttle people under the convention center to the other side. It's a route that remains walkable above ground, where a moving sidewalk would have been a better solution. 

Taken on its own, the first tunnel is using a flamethrower to light the candles on a birthday cake. But this early piece is just the beginning of a massive system that will connect the convention center to all the major casinos on the Las Vegas Strip.

Boring Co.'s huge plan for its underground tunnel network will not just connect the Strip to the convention center but will also bring passengers to Harry Reid Airport and Allegiant Stadium, the home of the Las Vegas Raiders. That's a bold vision that's being built now, but it's not the full plan.

Now, the Las Vegas City Council has approved a plan to expand the underground tunnel system to include the downtown Fremont Street area, the Las Vegas Review-Journal reported.   

Las Vegas has two major casino districts. There's the Strip, where Caesars Entertainment (CZR) - Get Caesars Entertainment Inc. Report , MGM Resorts International (MGM) - Get MGM Resorts International Report , and Wynn Resorts (WYNN) - Get Wynn Resorts Limited Report dominate with glitzy megaresorts. And there's the Fremont Street area, which is more evocative of old-school Las Vegas. 

The two areas are only a few miles apart, but on a busy night the trip between them can take half an hour due to traffic.

Boring Co. can solve that with its tunnel network and the Las Vegas City Council has approved five downtown stops.

"In total the Vegas Loop will be a 34-mile tunnel network with about 55 stations including Harry Reid International Airport and Allegiant Stadium," the paper reported. 

"Around 5 miles of tunnels and at least five stations will be included in the downtown area. The downtown stations include the Strat, Fremont Street Experience, the Slotzilla attraction, the Garage Mahal at the Circa Resort and the Plaza Hotel."

Additional stations could be added in the future. The downtown expansion will begin at some point in 2023.