December in Seoul is very cold, often below 0°C at night; snow can fall but isn't guaranteed — January is more likely.
- For guaranteed snow, head to the Gangwon mountains (Pyeongchang ski areas) or Nami Island.
- Dress in layers: thermal base, sweater, long padded coat; bring gloves, scarf and a beanie.
- Indoors and on trains it's warm, so choose a coat that's easy to take off.
- Wear non-slip shoes, as pavements can ice over.
Note: wind chill makes it feel colder than the temperature; check the "feels like" forecast before heading out.