There are several underground spaces where people work, and live. Chicago, Toronto both have underground systems. There is a town in Australia that half the people live underground because it’s so hot.

Some issues with underground spaces; it can be expensive to dig the proper tunnels, you have to make sure the geological make up of the area will support the structure, water draining down from above after rain storms can cause issues, and the big one is ventilation, you have to be able to move air through out the entire system.