Always good to have IotDs of people in joy. These S. Koreans are participating in the seventh annual Boryeong Mud Festival in Daecheon.
Looks like the mud there is grayish? Googling for the festival finds the following speculations about it:
The mud from Boryeong radiates long infrared rays and contains minerals, germanium and bentonite an indispensable cosmetic constituent. Also, cleansing form stimulates blood circulation, slow aging, reduces wrinkles and removes excess oil and dirt from your skin.
REMOVES excess dirt? Anyway, it looks like the festival has become a focus of tourism, as well as promoting the cosmetic qualities of the stuff. One
story suggested that the town developed it as an international event by making sure there were lots of photos of foreigners, "English teachers" - which, it would appear, make up a large number of the foreigners there at the moment.