Thanks. But what aren't those lounges located in the departure level? How do I get into the city (which requires passport control) after using the lounge there?
Simply pass through immigration and go to the train station or find a taxi.
I'm assuming from your post that you are traveling in Y, but if you are flying in C or F then your best best is the Welcome Lounge. Lots of info here:
LH to open new "Welcome" arrivals lounge in FRA