We visited and enjoyed the Taunus Therme while staying in Frankfurt - took the train from the city to Bad Homburg and walked from there - only about 15 minutes through a lovely park on the way. Thanks google maps for the excellent guidance.
We bought entry for 3 hours which we ended up using easily. Hired towels there - could take one if you have them but either way. Would recommend taking thongs (Aussies) or slides to walk around in.
You get a token at the entry and have to leave a deposit which you get back from the receptionist as you leave - take the token to the locker room and it slides into a wrist band that locks the locker and you keep with you for purchases.
Nice pools and spas downstairs. We paid the extra (€2??) for the sauna area upstairs which is textile (clothing) free - you keep your towel with you. Lots of different options for saunas - temperature, aroma, dry and steam, infrared, spas and pools and an outdoor area.
You can also hire robes - maybe more useful if you’re staying downstairs - but hey it’s Germany - skip those and head upstairs and enjoy.
We went on a weekday afternoon in May so was not overly busy.
On the way out, you go to the machine and put the token in to pay for any purchases, then to reception with your token for your deposit and exit.
As English speakers we didn’t have a lot of information from the signs - I hope some of this info may help you out! Would definitely recommend a visit.