Sapporo Ramen (Sanpachi Ramen), Nampo-dong
The big Japanese Ramen chain さんぱち has opened a branch in Nampo-dong. Of course, there are many Japanese-style ramen shops in the Gukje market, and while I can't say which is the best, this is not a bad place to start looking. My preference is for tonko ramen (ramen with pork slices), and Sapporo Ramen has a great selection.
Unfortunately I didn't spot any miso-style ramen on the menu, but both their salt and soy-sauce styles (the two main styles of ramen) were pretty good.
They also serve some izakaya favourites, such as gyoza (Japanese style 만두) and karoage (fried chicken balls), but these side dishes are only available after 6pm.
Location: On the main street in front of the new lotte department store. Be aware that although the big english sign says Sapporo Ramen, the place is signed as "sanpachi" in both Korean and Japanese.
Beer (hite): 3,000
English menu: No. Staff speak no English... but some do speak Japanese.
Vegetarian options: No.