Being on the eastern coast of the peninsula, there is no shortage of good seafood restaurants here, but the regional specialty is daegae (snow crab). Because of their size and popularity, they're quite expensive -- W70,000 to W120,000 for a meal. You'll start with gaejang (raw crab seasoned with sesame oil, salt, chile powder, and so on) and finish off the meal with daegae tahng (a hot pot of crab and other seafood).
A good place that specializes in crab and other seafood from the area is the Haedong Sanghwae Daegae Maeul (tel. 054/781-1585; 32-48 Beonji, Jukbyeon-li, Jukbyeon-myeon, Uljin-gun), located inside the Jukbyeon Seafood Market.
For hwae, try Namdo Hwae Iyagi (tel. 054/782-2090, 125-7 Nagok-li, Buk-myeon), which is located overlooking the beach and is open daily from 8:30am to 10pm. Also, there's a cropping of seafood restaurants in the alley behind the Uljin Shijang (tel. 054/783-2988), where you can see vendors hawk their catch of the day, as well as fresh songi mushrooms from nearby mountains.
