Monster, one in northerly German city (6)
I believe the answer is:
nessie
'monster' is the definition.
(Nessie is an example)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for nessie that I've seen before include "Scots loch monster (colloq.)" , "Nickname for a Scottish monster" , "Supposed loch monster" .)