Do you have to get naked at a Korean spa?

Yes!
Unlike the poultice rooms, this area is gender-segregated.
You must, however, be completely naked.
It may appear scary at first, but being around bodies of all shapes, sizes, and colors in an environment that isn't sexualized or airbrushed can be a genuinely body-positive and affirming experience. Plus, it's difficult to remain uneasy while everyone else is relaxed.