Plot german cities in ggplot R

Question

My apologies for my newbie question. I am so new to maps and quite lost at the vast info of internet.

I want to plot two german cities, Cologne and Berlin, in separate plots with ggplot2.

For now I only find the world data,

world <- map_data("world")
world

ggplot() +
  geom_map(
    data = world, map = world,
    aes(long, lat, map_id = region)
  ) 

Does anyone have a clue where and how I can find the data for these two cities?

thank you for your time