This is one of Berlin's most well known imbiss (snack bars), serving all sorts of German street food treats, including of course the currywurst. Strangely enough - for food that would be best eaten after several steins - this place closes mid evening.
Konnopke's Imbiss mentions around the internet
"...the sausage stand known as Konnopke's Imbiss has them all beat in terms of location and historical location." ...Full review at Eat Before You Die
"The simple snack shack is located below the tracks of the Eberswalder Strasse U-Bahn station and is run by the Ziervogel family, whose forefathers started selling their famous sausages on this spot in 1930." ...Full review at Guardian