The high-speed line from Hanover to Berlin bypasses Braunschweig, going a bit more to the north via Lehrte and Wolfsburg instead (although ICEs on the line manage to miss Wolfsburg surprisingly often, since only some of them are scheduled to stop there). As a result, you don't see a lot of long-distance passenger trains in Braunschweig. That does not mean it's boring, though: Braunschweig central station is a stop along a major east-west freight route. Wait there a bit, and you'll see lots of trains. And every now and then, you'll see something weird. Such as a class 218 in the original dark red livery with original old logos, speeding through at near track speed.
DB has tried forming several Regional Network companies, smaller with less bureaucracy, to compete more effectively with the then-new private railroads. Kurhessenbahn (Electorate of Hesse Railway) was the first. They also do some freight, and for that they needed a locomotive. Choosing a class 218 was very straightforward - DB has little else in that power category, thanks to a lack of new orders that has been going on for decades. But since they were all independent, they decided to not use the modern paint scheme. Instead, they brought it back into early Era IV paint, making it a prime target for rail photographers all over the country. And since they like to hire it out for special trains, it tends to appear all over the country. Braunschweig is really not that far from the historic Landgraviate of Hesse-Cassel, after which the line is named, all things considered.