On December 18, 1948 suppression forces discovered a cave near Darangshi Oreum. After tossing a grenade into the cave they ordered those hiding in the cave to come out. The hiding Jeju residents knew that coming out almost assuredly meant certain death and did not respond. In response the suppression forces lit a fire in the cave's entrance and blocked off the entrance leaving the cave to fill with smoke, causing the people inside to suffocate to death.

While incredibly tragic and cruel, the Darangshi Cave incident is more well-known because of the impact it had on Korean society when it was discovered and announced in 1991 and 1992. Until that point, the South Korean government had either denied that anything improper had been done during the 4.3 Incident ("it was an armed communist uprising that was dealt with accordingly") or simply denied it ("there were no massacres or killings of civilians"). Discussion of 4.3 was highly taboo due to the supposed connection to communism as well.

So, when the researchers discovered the caves and the remains of the dead inside (10 sets of remains), they knew that if they played their cards in the right way, they could force the government to finally admit to what happened. Instead of announcing their finding right away or notifying the government (then the Roh Taewoo administration - 노태우정부) they quietly began to contact the media and lawyers. Once they had their media stories lined up and were secure in the knowledge that they were on firm legal ground, the researchers released the news and images.

The government (while democratically elected was still in the tradition of the previous military dictatorships) tried to cover the story up. They destroyed the entrance to the cave and pushed the families to cremate the bodies and scatter the ashes in the sea within days of the story breaking. However, the proverbial genie was out of the bottle and it was too late. The general population now was fully aware that the government had not been truthful about the 4.3 Incident and had tried to cover up what they had done.

References

Jeju 4.3 Archives - "다랑쉬굴" (readable here in Korean)

The Jeju Massacre - "Darangshi Cave" (readable here in English)

Jeju Dark Tours - "Darangshi Cave" (readable here in English)