Mogyokso is a very small body of water in a brook at <a href="https://en.wikipedia.org/wiki/Songnisan" class="extiw" title="w:Songnisan">Songnisan</a>, a mountain in South Korea.  It is said that Sejo, the 7th king of the Joseon dynasty, washed in here, where it purified the boils on his skin.
<a href="//commons.wikimedia.org/wiki/User:YooChung" title="User:YooChung">Yoo Chung</a>
CC BY-SA 2.5
<span class="int-own-work" lang="en">Own work</span>