However when I googled it, Wikipedia says it is 'pork bone soup'. SO, I guess maybe it can be made with any type of pork bones? Who knows. All I know is it is good and if you like Korean food then you should try this.
The Gamjatang place is RIGHT ACROSS THE STREET.
Take note: The orange sign says 감자탕
Go in that alley.
Check out the menu, they even have it highlighted with red around what you need to order.
감자탕 = 6,000 won.
Neckbone soup - pork neck bone, vegetables, green onions, hot peppers (although this was not very spicy at all), potatoes and wild sesame seeds. You will need to eat this with chopsticks and a spoon. Chopsticks to pick the very tender meat out with, a spoon to eat the delicious broth.
Exit Commissary gate - turn left
Stay right - Turn right onto Itaewon Street
Turn left on Daesagwan-ro - this street has a light.
(You will be going through a street with many lights and lots of people walking - near Hannam Village)
At the light pretty far down just before you come to the big intersection (Daesagwan-ro) turn left a - it's kind of a crazy light - I think it is just flashing, maybe not even a light at all - but more of a 4 way stop.
The restaurant is on your left just a few stores down.
Park on the street.