Many German clubs' match tickets include free travel on public transport for typically 3 hours before the game until the end of operations that day. This will typically be for travel anywhere within the regional transport network in which the club is located. That means you could stay out of town and still travel to and from the game for free. So, it'll be useful to know which towns are covered by each network. That's what I've listed here (along with direct links to the Booking.com hotels page for each of those out-of-town locations). It's a list originally put together for Euro 2024, so the main cities covered are those that hosted tournament games.

Hamburger Verkehrsverbund - HVV (city: Hamburg; website: HVV)
HVV network map
One of the smaller transport networks offering the 36 hours of free travel. Includes Itzehoe, Stade, Buxtehude, Soltau, Lüneburg, Dannenberg, Büchen, and Bad Oldesloe.

Verkehrsverbund Berlin-Brandenburg - VBB (city: Berlin; website: VBB)
VBB network map
Out-of-town locations covered include: Angermünde, Nauen, Rathenow, Brandenurg, Potsdam, Bad Belzig, Jüterbog, Elsterwerda, Cottbus, and Frankfurt (Oder).

Mitteldeutscher Verkehrsverbund - MDV (city: Leipzig; website: MDV)
MDV network map
Includes Halle, Dessau, Naumburg, Altenburg, Colditz, Döbeln, Oschatz, Torgau, and Lutherstadt Wittenberg.

Rhein-Main-Verkehrsverbund - RMV (city: Frankfurt; website: RMV)
RMV network map
Includes: Marburg, Dillenburg, Limburg, Wiesbaden, Mainz, Bingen, Worms, Darmstadt, Aschaffenburg, Offenbach, Hanau, and Fulda.

Verkehrs- und Tarifverbund Stuttgart - VVS (city:Stuttgart; website: VVS)
VVS network map
Like Hamburg, a relatively small network that doesn't extend much beyond 'Greater Stuttgart'. Includes: Marbach, Ludwigsburg, Bietigheim-Bissingen, Weil der Stadt, Böblingen, Filderstadt, Neidlingen, Ostfildern, Kirchheim, Schorndorf, and Backnang.

Münchner Verkehrs- und Tarifverbund - MVV (city: Munich; website: MVV)
MVV network map
Mainly just 'Greater Munich'. Includes: Freising, Petershausen, Herrsching, Tutzing, Wolfratshausen, Holzkirchen, Ebersberg, and Erding.

Verkehrsverbund Rhein-Sieg - VRS (city: Cologne; VRS)
VRS network map
Includes Leverkusen, Kerpen, Erftstadt, Dahlem, Euskirchen, Bonn, Königswinter, Windeck, and Marienhelde.

Verkehrsverbund Rhein-Ruhr - VRR (cities: Dortmund, Gelsenkirchen and Düsseldorf; website: VRR).
VRR network map
The big one! Includes: Bochum, Herne, Mönchengladbach, Oberhausen, Solingen, Bottrop, Duisburg, Essen, Hagen, Krefeld, Mülheim an der Ruhr, Remscheid, Wuppertal, Kleve, Recklinghausen and Wesel.