Montreal, Quebec, Underground City, or la ville souterraine in French, is the largest habitable underground network in the world. Its 32 km (20 mi) of tunnel cover more than 41 city blocks (about 12 km2 (5 sq mi)). https://en.m.wikipedia.org/wiki/Underground_city#:~:text=Montreal%2C%20Quebec%2C%20Underground%20City%2C,2%20(5%20sq%20mi)).