Underground construction

Underground construction is building things by digging down into the ground instead of building up. Instead of building buildings or houses above ground, workers dig down deep into the ground and make something inside the hole. It's kind of like a tunnel, but with walls built to make a space. People might use underground construction if they want to build something but don't have enough space on the ground. For example, a city might need to build more roads, but they don't have enough ground level space to build them, so they have to go underground.