Die Zentrale coworking in Frankfurt is centrally located and has a Nomad monthly membership for around 120 euro. They offer nice coffee, meeting room access. Neat and well lit co-working space with both local startups and Digital Nomads. Frankfurt also has a nice WeWork which is much more expensive though.
TechQuartier is a very popular startup ecosystem Co-working space. Sorted by city, University and other sponsors, practically located near Convention centre, main train station and big shopping mall with food court: Skyplaza. Very nice staff, management and owners.