Cheong Jin Ok

This cult restaurant is no. 46 on CNN's top 50 list of why Seoul is the greatest city in the world. The reason? their hangover soup. It is the only thing they have on the menu and Seoul office workers, being notorious drinkers, crave this traditional hangover cure meal on their way home from company dinner or the day after for lunch. 

Jongno district is actually home to a number of famous haejangguk restaurants, and Cheongjinok is considered the forerunner among them. It pened in 1937, and the restaurant has been run by three generations of the same family. 
Beef bones are simmered for more than 24 hours to make a rich broth, and soybean paste 
is added to neutralize the meaty odor. Ingredients added to the 
broth include various vegetables, clotted beef blood, beef intestines, and rice. This restaurant is ALWAYS crowded.

Try it if you want a unique food experience or if you're simply hungover! 

For more info: http://www.cheongjinok.com/english

24 hour open all year.