Ok, this restaurant full name is "SmorGas Viking Style Buffet", I have no idea why. I guess I don't know enough about viking gastronomy. Anyhow, it was quite good! But pricey... It's located in Seoul Royal Hotel, at the 21st floor. For 40,000 won, you have unlimited access to the buffet + unlimited beer (I think for the beer it's only during the weekdays evening).