I’ve mentioned Autobahnkirchen before.
Here’s the one at Medenbach near Frankfurt am Main:
They had a useful brochure showing all the motorway churches in Germany. You can see them here – Medenbach is number 16. I’m sorry I missed the right turn-off for number 20, which I also passed – it’s more impressive than I realized, but also in the middle of the heavy goods vehicle services station, and you can scarcely move for lorries on Sundays and public holidays.