why did the black plague spare some cites in germany?

Answer 1

The Black Plague (Bubonic Plague) was spread by fleas, rats, and people infected with the plague. There were many cities in germany that had indoor plumbing, sewar systems, and were extremely sanitary. During this era in other parts of Europe it was common to have farm animals, and other domestic animals in ones house (this way no one could steal them at night), these animals had fleas and the flea bites spread the disease. For the cities that did not have indoor plumbing, open sewars, or people just threw the pot out the window when it was full, this attracted the rats whose fleas continued to spread the plague. Lastly, cleanliness was not observed as it is today, so people might take a bath once or twice a year, this too hindered them. Lastly, many of those cities that weren't infected totally were probably in the northern reaches of Germany or in mountainous areas that were difficult to reach. The freezing cold killed fleas and animals infected, it also helped to kill some of the plague, but not all. Cities probably walled themselves off from outsiders to protect themselves from the plague and only allowed clean people to enter.
Remember:
"Ring around the rosy,
Pocket full of posy,
Ashes, Ashes,
We all fall down."

Answer 2

I can only venture a guess and I'm not sure if there were specific cities excluded from the plague. Look at a map of Germany and we will see that many cities have "Bad" in the name which means "Bath" in English. Many whorehouses, taverns and health spas all offered hot-water bathing for relaxation.