It's a taco spot inside Cheongnyangni Gyeongdong Market.
I heard it's run by the same owner as La Caye, a famous taco place in Sindang, and this place specializes in seafood tacos.
The space is really unique and cool, but above all it was so incredibly tasty that I ate in a hurry without realizing it and then felt disappointed wondering why it was gone so quickly.
The downsides are that it's quite expensive and a little far—other than that, there's not much to complain about. The staff were friendly! It's a bit far, but definitely worth the trip!