This is the 759th most frequent German word.
bremen
"Bremen" is a proper noun referring to a city in northern Germany.
Here, 'Bremen' is used as the name of a city in Germany, indicating the destination.
Ich fahre morgen nach Bremen.
I'm traveling to Bremen tomorrow.
'Bremer' is an adjective derived from 'Bremen', used to describe something related to the city, here indicating the origin of the musicians.
Die Bremer Stadtmusikanten sind ein berühmtes Märchen.
The Town Musicians of Bremen is a famous fairy tale.
In this context, 'Bremen' denotes the city itself and its unique political and historical status as a free Hanseatic city.