I saw currywurst stands all over Berlin and some in Hamburg, too. Thinking it was a sausage with curry in the dog, I tried them at different locations. The sausage is a basic sausage, the curry is in the tomatoe sauce. The behind the scenes story is, after the war, Herta Heuwer living in Berlin, made a ketsup sauce with curry and other spices to pour on a cheap piece of pork. People loved it and that’s how it became a currywurst.
The best I had was served at KaDeWe gourmet food dept and next best was from Dom’s currywurst owned by Berlin Hilton. I liked the ketusp sauce best at KaDeWe with dashes of paprika and fried onion strips on top. They are reasonably priced and fill the stomach, especially with french fries which is the typical meal.