Spa towns near Munich

Spa town Bad Tölz is located 50 km South of Munich (summer activities).

Therme Erding is a large spa venue North-West of Munich.

Use trains: https://int.bahn.de/en

Therme Erding is fine if you're staying in Munich. While in Munich, I would also recommend a visit to the Müller'sches Volksbad. A superb Art Nouveau public bath with massage and steam bath options. It's not really spa, but it's a great experience. https://www.muenchen.de/en/culture-leisure/mullersches-volksbad

Otherwise, I would recommend:
Therme Bad Aibling
Kristall Therme trimini Kochel am See
Hotel Sommer Füssen (I sometimes spend a few days there)
Rupertus Therme Bad Reichenhall
Rottal Therme Bad Birnbach
Kristall Therme Schwangau

I either know the Spas myself or have heard good things about them. Nevertheless, I would of course recommend doing your own research to be sure that it fits. Things can change.

Dont know where your Danube river trip ends but see

Bad Füssing 30 min from Passau towards Munich with

Europa Therme https://www.europatherme.de/
and
Therme eins https://www.thermeeins.de/

Following the roads to Munich see towns like

Burghausen (largest castle of Germany)
https://www.burg-burghausen.de/englisch/tourist/index.htm

Altötting (church)
https://www.gnadenort-altoetting.de/kirchen-kultur/gnadenkapelle

Wasserburg am Inn
https://www.wasserburg.de/en/sightseeing/impressions

and more

Erding is the biggest anywhere, on a weekend it attracts a lot of children because of the wave pool and all the water slides.

We don't do any of that yet we like it very much there. Easy by train, easy by car. It is so huge it is easy to leave the kids behind and find quieter areas. I highlight the "er" for a reason.

Erding is north-east not northwest of central Munich at the end of the S-Bahn.

I often recommend Therme Erding for people who have kids, but a quiet place close to nature it is not.

Bad Tolz is very nice, and there used to be a large US military presence in the town.

I'll add to the list so far with Seebad Starnberg, which has a nice view of the See, and Therme Bad Aibling.

If you want to try something else there's Kristall Palm Beach an hour north in Nuremberg. I have not been there in many years, but it used to be a very good place to spend a day.

Bad Tölz has been mentioned twice now. Even though it has "Bad" (bath) in its name, there's no longer a spa (thermal bath). Other than that, it's definitely a nice village. There's only one ordinary public bath left in Bad Tölz.

Heidi you could also just google "Therme". That will show you all the thermal baths. Or you can search for a hotel with a spa if you're looking for everything in one place.

visit a couple of spa towns before flying home from Munich

Please clarify. Where does your Danube trip end? And, you are planning to visit these towns over night or just daytrip from Munich. I try to visit at least one therme each week when in Germay. My favorite is in Berlin (Vabali), so probably not convenient.

Have to ask, you are familiar and comfortable with the textile free environment of German thermes?

Thank you for all the replies. I am comfortable with the “textile free environment”. Just adults, no children this trip.
I should clarify, we will be coming from Passau and plan to spend a night or two in these cities but will spend our last night in Munich before we fly out.

Thanks for clarifying. Most of my spa expereince have been further west and north than you will want to go.

As suggsted, have you looked at Bad Fussing? Just south of Passau. Never been there and I'm not sure how charming the town is or if the mega therme is what you are looking for.

Bad Tölz has been mentioned twice now. Even though it has "Bad" (bath) in its name, there's no longer a spa (thermal bath).

Mignon, Bad Tölz never had thermal water sources but healing water sources (natural iodine). The prefix "Bad" (spa) was used in German for all kinds of curing, some tows were climatic spas (e. g. North Sea) or salt spas moor spas. And OP was asking for spa towns in general.

@MarkK

I spent my childhood at the Alpamare in Bad Tölz because it was such a cool bath. But honestly, it doesn't matter whether it was ever a thermal spa or just a water park with a spa area or whatever. Excuse me, but this is really nitpicking and I can't stand these pedantic explanations at all, to be honest. I understood exactly what Heidi was asking for and what she was asking for is missing in Bad Tölz in the meantime.

And I apologize to Heidi, but I had to write this now.