That’s a wild but cool idea, but it’s not just a DIY “tunnel garage.” You’ll need to check the structural integrity, ventilation, and fire codes, and you’ll almost certainly need permits from the transit authority. If you can line it up with an urban‑innovation grant or a partnership with the city, the space could become a legit underground lab, but keep the bureaucracy in your back pocket—those guys are not exactly friendly to spontaneous tunnel projects. Just remember to bring a fire extinguisher and a lot of patience, because the paperwork will probably outpace the soldering.