The ancient Nonggyo Bridge in Jincheon is the oldest stone bridge found in South Korea. It's constructed of flat reddish rocks laid on the waterbed in a form that resembles fish scales, and also stepping stones lying over the rocks.
The most amusing fact is there is absolutely no cement, nor any other material. Despite constant water level fluctuations and time, the bridge demonstrates surprising longevity. Therefore, Nonggyo Bridge is deemed a kind of engineering marvel.