We traveled to Korea during Chuseok and it was very quiet though we had no issues finding great restaurants that remained open. The 3rd and 5th will be very quiet in Seoul as Seoulites leave town to visit their families. It'll be a lot like Christmas or Thanksgiving in a major city here in the US.

If you plan on traveling outside of Seoul during the 3 day holiday just be prepared for very crowded/sold out trains and roads.

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