Restaurants, a fire station, 30,000 employees and a 3.7 km long pedestrian tunnel... The largest factory in the world needs neither air conditioning in summer nor heating in winter

The Boeing factory in Everett, California is the largest in the world. In summer, if it gets too hot, the huge doors open to let in fresh air. And in winter, the number of employees (generally 10,000 are present at the same time), the neon lights, and the machines are enough to maintain a comfortable temperature.