February 18, 1959, was just an ordinary day for road workers in Lyon, France, tasked with building a tunnel under Croix-Rousse Hill in a bid to reduce traffic congestion. While drilling, they stumbled upon an old well. That wasn’t unusual. Though Lyon lay across two major rivers, access to drinking water was poor, and the city was peppered with wells. On closer inspection, however, the road workers discovered that this well didn’t simply descend vertically. Branching off from the shaft was a network of 32 identical tunnels, each about 100…
