Extracting all cities from a state using PostGIS

Question

I have written a PostGIS query on a database with OSM data of the state of Baden-Württemberg.

SELECT * 
FROM public.planet_osm_polygon 
WHERE boundary = 'administrative' 
  AND admin_level = '8';

So it turns out that not all cities/towns have an admin_level tag of 8. Is there any way we can further constrain the query to filter out only the towns/cities?