At a TED Talk in Vancouver Friday, Elon Musk admitted he has been “puttering around” with Hyperloop technology for a while now.

And although the Hyperloop test track was built at SpaceX in Hawthorne, California with the aim of encouraging students to come and attempt to improve the technology through a different kind of pod racing, he still considers it something of a hobby.

Still, that clearly hasn’t stopped him from scheming about how he could incorporate it into his latest obsession, the Boring Company. Musk has eluded to his interest in incorporating Hyperloop into his Boring Company Tunnel projects in the past, but on Friday he described in technical detail how the ultra-fast pod transport could be the perfect match for his tunnel-based system.

Conceptually, Boring Company’s aim is to create a vast network of tunnels underground to decrease gridlock and speed up city transportation. According to Musk, it turns out that these deeply dug tunnels can inherently accommodate Hyperloop’s vacuum.

“In order to seal against the water table, you’ve got to typically design a tunnel wall to be good to about five or six atmospheres,” Musk said. “To go to vacuum is only one atmosphere — or near-vacuum — so it sort of turns out automatically that if you build a tunnel that is good enough to resist the water table, it’s automatically capable of holding vacuum.” Insert Hyperloop.

When pressed by interviewer Chris Anderson about what length of Hyperloop tunnel he was tangibly envisioning, Musk answered characteristically that there really was no limit. “You could dig as much as you want,” he said. “I think if you were to do something like D.C. to New York Hyperloop, I think you’d probably want to go underground the entire way because it’s a high-density area.”

If massive underground construction sounds incredibly inconvenient, Musk was sure to remind the audience just how deep these tunnels would theoretically be. “If that tunnel is dug more than three or four tunnel diameters beneath your house, you will not be able to detect it being dug at all,” he said. “In fact, if you’re able to detect the tunnel being dug, whatever device you’re using, you can get a lot of money from that device from the Israeli military who is trying to detect tunnels from Hamas.”