Original vertical datum is the starting point of measuring the elevation of Korea’s national territory. This land facility was installed in 1963 by measuring the difference compared to mean level of the sea water. This original vertical datum allows us to compare the heights of Seoraksan Mountain in Gangwon-do and Hallasan Mountain in Jejudo Island. Hexagonal platform made with granite stone was laid on top of a circular bondstone, and an amethyst was inserted to indicate the original vertical datum, which is protected by a small cylindrical brick structure. The height of this point, which serves as standard for all level measurements in Korea, is 26.6871m.