I have been to Frankfurt many times on a Sunday night. I usually wind down my Europe trips there when I have to fly out of FRA back to the U.S. My favorite gay hotel to stay at is the Downtown-Frankfurt-Hotel (
[email protected]) on Schäfergasse 27. Schäfergasse is a little gay street with some bars. The hotel is upstairs from Lucky's (
http://www.luckys-lm27.de) which is a cafe bar. Download a map of Gay Frankfurt here:
http://www.gaymap.info/-download-map...ankfurt_09.pdf
Sunday nights in Frankfurt are low key. My favorite bar to end the night is The Stall (Stiftstr. 22), which is a very cruisy leather bar. The bartenders and patrons are always friendly.
The Metropol Sauna just opened up in 2008 and is very clean and modern. (
http://www.metropol-sauna.de/)
Both cities are low key on a Sunday night. If you want a more convenient airport then I would pick FRA.
If you go to MUC then check out NY Club Disco (Sonnenstr. 25) and Deutsche Eiche Sauna (Reichenbachstr. 13).