On May 18th, 1980, Korean students in Gwangju led a massive protest against South Korea's government (which was at the time a dictatorship), arguing in favor of a democratic government. Around 144 civilians ended up being killed during the suppression of this uprising, and many Koreans visit the cemetery memorial today to honor those that died during this protest.
Many people were traveling this weekend due to a national holiday: Children's Day! While this was unfortunate for me because of the traffic, many children were happy. It's common for kids to get presents and be taken on picnics or to amusement parks in celebration of the day. While I missed out on the celebrations in my own town, many of my friends posted pictures of fun celebrations happening where they were living in Korea.