The incident occurred during the Chuseok holiday and was shared online by a netizen, who was visiting the site with family, Korea Joongang Daily reported.
"It was very crowded, and there was a long line of people waiting," the post said. "Then I saw a woman seating her child on the ground to defecate. Because there were so many people watching, she moved slightly farther down and finished there."
The netizen expressed disbelief at the lack of intervention, noting that a tour guide appeared nearby but did not address the issue, even though others had witnessed the act, Maeil Business newspaper reported.
A photo attached to the post showed the woman crouching near the shoreline with her child, further fueling the backlash.
The post quickly spread across social media, triggering widespread criticism of the woman's behavior.
"How you behave in other countries speaks volumes about how you behave in your own country! This is not only shameful and disgusting but a massive disrespect to the monument and history of the country! I hope severe punishment is ordered," a netizen wrote.
"Arrest and 10 years prison," another wrote.
This incident is not the first of its kind in Jeju.
Last June, a foreign child was caught defecating on a street in Jeju City, which also led to public outrage.
Data from the Jeju Police Agency reveals a sharp rise in public disorder incidents involving foreign nationals.