서울 지하철 이렇게 만들어졌다
<iframe width="1280" height="960" src="https://www.youtube.com/embed/PN9OqjGTTeQ" title="서울 지하철 3·4호선 건설 (1984)" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" allowfullscreen></iframe>