This place that has appeared twice is Samsan branch in Incheon. You can view the photos inside the place on its official website. The scene outside was also filmed outside this restaurant.
This place is between Samsan Gymnasium Station (station on right side of map) and Gulpocheon Station (station on left side), you can walk there from both of the stations (exit 3 and 8 respectively).
한촌설렁탕 인천삼산점 韓村雪濃湯 仁川三山店
Hanchon Selleongtang Incheon Samsan Branch
地址 Address: 인천광역시 부평구 길주로 659 미라쥬타워
電話 Phone: 032-515-3690
(Pic Cr: tvN/viu)